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![Masahiro Yamada](/assets/img/avatar_default.png)
To enjoy driver-model on sandbox, using device tree is recommended. While we are here, change sandbox_config to sandbox_defconfig too. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Acked-by: Simon Glass <sjg@chromium.org> Acked-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
805 lines
30 KiB
Plaintext
805 lines
30 KiB
Plaintext
Driver Model
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============
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This README contains high-level information about driver model, a unified
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way of declaring and accessing drivers in U-Boot. The original work was done
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by:
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Marek Vasut <marex@denx.de>
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Pavel Herrmann <morpheus.ibis@gmail.com>
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Viktor Křivák <viktor.krivak@gmail.com>
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Tomas Hlavacek <tmshlvck@gmail.com>
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This has been both simplified and extended into the current implementation
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by:
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Simon Glass <sjg@chromium.org>
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Terminology
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-----------
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Uclass - a group of devices which operate in the same way. A uclass provides
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a way of accessing individual devices within the group, but always
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using the same interface. For example a GPIO uclass provides
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operations for get/set value. An I2C uclass may have 10 I2C ports,
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4 with one driver, and 6 with another.
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Driver - some code which talks to a peripheral and presents a higher-level
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interface to it.
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Device - an instance of a driver, tied to a particular port or peripheral.
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How to try it
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-------------
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Build U-Boot sandbox and run it:
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make sandbox_defconfig
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make
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./u-boot -d u-boot.dtb
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(type 'reset' to exit U-Boot)
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There is a uclass called 'demo'. This uclass handles
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saying hello, and reporting its status. There are two drivers in this
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uclass:
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- simple: Just prints a message for hello, doesn't implement status
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- shape: Prints shapes and reports number of characters printed as status
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The demo class is pretty simple, but not trivial. The intention is that it
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can be used for testing, so it will implement all driver model features and
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provide good code coverage of them. It does have multiple drivers, it
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handles parameter data and platdata (data which tells the driver how
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to operate on a particular platform) and it uses private driver data.
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To try it, see the example session below:
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=>demo hello 1
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Hello '@' from 07981110: red 4
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=>demo status 2
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Status: 0
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=>demo hello 2
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g
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r@
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e@@
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e@@@
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n@@@@
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g@@@@@
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=>demo status 2
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Status: 21
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=>demo hello 4 ^
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y^^^
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e^^^^^
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l^^^^^^^
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l^^^^^^^
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o^^^^^
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w^^^
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=>demo status 4
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Status: 36
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=>
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Running the tests
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-----------------
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The intent with driver model is that the core portion has 100% test coverage
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in sandbox, and every uclass has its own test. As a move towards this, tests
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are provided in test/dm. To run them, try:
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./test/dm/test-dm.sh
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You should see something like this:
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<...U-Boot banner...>
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Running 29 driver model tests
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Test: dm_test_autobind
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Test: dm_test_autoprobe
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Test: dm_test_bus_children
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Device 'd-test': seq 3 is in use by 'b-test'
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Device 'c-test@0': seq 0 is in use by 'a-test'
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Device 'c-test@1': seq 1 is in use by 'd-test'
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Test: dm_test_bus_children_funcs
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Test: dm_test_bus_children_iterators
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Test: dm_test_bus_parent_data
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Test: dm_test_bus_parent_ops
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Test: dm_test_children
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Test: dm_test_fdt
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Device 'd-test': seq 3 is in use by 'b-test'
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Test: dm_test_fdt_offset
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Test: dm_test_fdt_pre_reloc
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Test: dm_test_fdt_uclass_seq
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Device 'd-test': seq 3 is in use by 'b-test'
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Device 'a-test': seq 0 is in use by 'd-test'
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Test: dm_test_gpio
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extra-gpios: get_value: error: gpio b5 not reserved
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Test: dm_test_gpio_anon
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Test: dm_test_gpio_copy
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Test: dm_test_gpio_leak
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extra-gpios: get_value: error: gpio b5 not reserved
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Test: dm_test_gpio_requestf
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Test: dm_test_leak
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Test: dm_test_lifecycle
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Test: dm_test_operations
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Test: dm_test_ordering
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Test: dm_test_platdata
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Test: dm_test_pre_reloc
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Test: dm_test_remove
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Test: dm_test_spi_find
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Invalid chip select 0:0 (err=-19)
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SF: Failed to get idcodes
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Device 'name-emul': seq 0 is in use by 'name-emul'
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SF: Detected M25P16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
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Test: dm_test_spi_flash
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2097152 bytes written in 0 ms
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SF: Detected M25P16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
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SPI flash test:
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0 erase: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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1 check: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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2 write: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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3 read: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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Test passed
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0 erase: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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1 check: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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2 write: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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3 read: 0 ticks, 65536000 KiB/s 524288.000 Mbps
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Test: dm_test_spi_xfer
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SF: Detected M25P16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
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Test: dm_test_uclass
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Test: dm_test_uclass_before_ready
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Failures: 0
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What is going on?
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-----------------
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Let's start at the top. The demo command is in common/cmd_demo.c. It does
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the usual command processing and then:
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struct udevice *demo_dev;
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ret = uclass_get_device(UCLASS_DEMO, devnum, &demo_dev);
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UCLASS_DEMO means the class of devices which implement 'demo'. Other
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classes might be MMC, or GPIO, hashing or serial. The idea is that the
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devices in the class all share a particular way of working. The class
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presents a unified view of all these devices to U-Boot.
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This function looks up a device for the demo uclass. Given a device
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number we can find the device because all devices have registered with
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the UCLASS_DEMO uclass.
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The device is automatically activated ready for use by uclass_get_device().
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Now that we have the device we can do things like:
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return demo_hello(demo_dev, ch);
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This function is in the demo uclass. It takes care of calling the 'hello'
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method of the relevant driver. Bearing in mind that there are two drivers,
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this particular device may use one or other of them.
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The code for demo_hello() is in drivers/demo/demo-uclass.c:
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int demo_hello(struct udevice *dev, int ch)
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{
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const struct demo_ops *ops = device_get_ops(dev);
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if (!ops->hello)
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return -ENOSYS;
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return ops->hello(dev, ch);
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}
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As you can see it just calls the relevant driver method. One of these is
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in drivers/demo/demo-simple.c:
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static int simple_hello(struct udevice *dev, int ch)
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{
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const struct dm_demo_pdata *pdata = dev_get_platdata(dev);
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printf("Hello from %08x: %s %d\n", map_to_sysmem(dev),
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pdata->colour, pdata->sides);
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return 0;
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}
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So that is a trip from top (command execution) to bottom (driver action)
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but it leaves a lot of topics to address.
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Declaring Drivers
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-----------------
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A driver declaration looks something like this (see
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drivers/demo/demo-shape.c):
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static const struct demo_ops shape_ops = {
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.hello = shape_hello,
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.status = shape_status,
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};
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U_BOOT_DRIVER(demo_shape_drv) = {
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.name = "demo_shape_drv",
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.id = UCLASS_DEMO,
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.ops = &shape_ops,
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.priv_data_size = sizeof(struct shape_data),
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};
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This driver has two methods (hello and status) and requires a bit of
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private data (accessible through dev_get_priv(dev) once the driver has
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been probed). It is a member of UCLASS_DEMO so will register itself
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there.
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In U_BOOT_DRIVER it is also possible to specify special methods for bind
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and unbind, and these are called at appropriate times. For many drivers
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it is hoped that only 'probe' and 'remove' will be needed.
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The U_BOOT_DRIVER macro creates a data structure accessible from C,
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so driver model can find the drivers that are available.
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The methods a device can provide are documented in the device.h header.
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Briefly, they are:
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bind - make the driver model aware of a device (bind it to its driver)
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unbind - make the driver model forget the device
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ofdata_to_platdata - convert device tree data to platdata - see later
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probe - make a device ready for use
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remove - remove a device so it cannot be used until probed again
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The sequence to get a device to work is bind, ofdata_to_platdata (if using
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device tree) and probe.
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Platform Data
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-------------
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Platform data is like Linux platform data, if you are familiar with that.
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It provides the board-specific information to start up a device.
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Why is this information not just stored in the device driver itself? The
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idea is that the device driver is generic, and can in principle operate on
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any board that has that type of device. For example, with modern
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highly-complex SoCs it is common for the IP to come from an IP vendor, and
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therefore (for example) the MMC controller may be the same on chips from
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different vendors. It makes no sense to write independent drivers for the
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MMC controller on each vendor's SoC, when they are all almost the same.
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Similarly, we may have 6 UARTs in an SoC, all of which are mostly the same,
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but lie at different addresses in the address space.
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Using the UART example, we have a single driver and it is instantiated 6
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times by supplying 6 lots of platform data. Each lot of platform data
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gives the driver name and a pointer to a structure containing information
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about this instance - e.g. the address of the register space. It may be that
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one of the UARTS supports RS-485 operation - this can be added as a flag in
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the platform data, which is set for this one port and clear for the rest.
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Think of your driver as a generic piece of code which knows how to talk to
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a device, but needs to know where it is, any variant/option information and
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so on. Platform data provides this link between the generic piece of code
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and the specific way it is bound on a particular board.
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Examples of platform data include:
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- The base address of the IP block's register space
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- Configuration options, like:
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- the SPI polarity and maximum speed for a SPI controller
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- the I2C speed to use for an I2C device
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- the number of GPIOs available in a GPIO device
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Where does the platform data come from? It is either held in a structure
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which is compiled into U-Boot, or it can be parsed from the Device Tree
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(see 'Device Tree' below).
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For an example of how it can be compiled in, see demo-pdata.c which
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sets up a table of driver names and their associated platform data.
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The data can be interpreted by the drivers however they like - it is
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basically a communication scheme between the board-specific code and
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the generic drivers, which are intended to work on any board.
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Drivers can access their data via dev->info->platdata. Here is
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the declaration for the platform data, which would normally appear
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in the board file.
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static const struct dm_demo_cdata red_square = {
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.colour = "red",
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.sides = 4.
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};
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static const struct driver_info info[] = {
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{
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.name = "demo_shape_drv",
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.platdata = &red_square,
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},
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};
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demo1 = driver_bind(root, &info[0]);
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Device Tree
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-----------
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While platdata is useful, a more flexible way of providing device data is
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by using device tree. With device tree we replace the above code with the
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following device tree fragment:
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red-square {
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compatible = "demo-shape";
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colour = "red";
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sides = <4>;
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};
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This means that instead of having lots of U_BOOT_DEVICE() declarations in
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the board file, we put these in the device tree. This approach allows a lot
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more generality, since the same board file can support many types of boards
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(e,g. with the same SoC) just by using different device trees. An added
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benefit is that the Linux device tree can be used, thus further simplifying
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the task of board-bring up either for U-Boot or Linux devs (whoever gets to
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the board first!).
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The easiest way to make this work it to add a few members to the driver:
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.platdata_auto_alloc_size = sizeof(struct dm_test_pdata),
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.ofdata_to_platdata = testfdt_ofdata_to_platdata,
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The 'auto_alloc' feature allowed space for the platdata to be allocated
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and zeroed before the driver's ofdata_to_platdata() method is called. The
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ofdata_to_platdata() method, which the driver write supplies, should parse
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the device tree node for this device and place it in dev->platdata. Thus
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when the probe method is called later (to set up the device ready for use)
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the platform data will be present.
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Note that both methods are optional. If you provide an ofdata_to_platdata
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method then it will be called first (during activation). If you provide a
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probe method it will be called next. See Driver Lifecycle below for more
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details.
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If you don't want to have the platdata automatically allocated then you
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can leave out platdata_auto_alloc_size. In this case you can use malloc
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in your ofdata_to_platdata (or probe) method to allocate the required memory,
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and you should free it in the remove method.
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Declaring Uclasses
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------------------
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The demo uclass is declared like this:
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U_BOOT_CLASS(demo) = {
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.id = UCLASS_DEMO,
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};
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It is also possible to specify special methods for probe, etc. The uclass
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numbering comes from include/dm/uclass.h. To add a new uclass, add to the
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end of the enum there, then declare your uclass as above.
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Device Sequence Numbers
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-----------------------
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U-Boot numbers devices from 0 in many situations, such as in the command
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line for I2C and SPI buses, and the device names for serial ports (serial0,
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serial1, ...). Driver model supports this numbering and permits devices
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to be locating by their 'sequence'. This numbering unique identifies a
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device in its uclass, so no two devices within a particular uclass can have
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the same sequence number.
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Sequence numbers start from 0 but gaps are permitted. For example, a board
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may have I2C buses 0, 1, 4, 5 but no 2 or 3. The choice of how devices are
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numbered is up to a particular board, and may be set by the SoC in some
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cases. While it might be tempting to automatically renumber the devices
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where there are gaps in the sequence, this can lead to confusion and is
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not the way that U-Boot works.
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Each device can request a sequence number. If none is required then the
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device will be automatically allocated the next available sequence number.
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To specify the sequence number in the device tree an alias is typically
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used.
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aliases {
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serial2 = "/serial@22230000";
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};
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This indicates that in the uclass called "serial", the named node
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("/serial@22230000") will be given sequence number 2. Any command or driver
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which requests serial device 2 will obtain this device.
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Some devices represent buses where the devices on the bus are numbered or
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addressed. For example, SPI typically numbers its slaves from 0, and I2C
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uses a 7-bit address. In these cases the 'reg' property of the subnode is
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used, for example:
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{
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aliases {
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spi2 = "/spi@22300000";
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};
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spi@22300000 {
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#address-cells = <1>;
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#size-cells = <1>;
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spi-flash@0 {
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reg = <0>;
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...
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}
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eeprom@1 {
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reg = <1>;
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};
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};
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In this case we have a SPI bus with two slaves at 0 and 1. The SPI bus
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itself is numbered 2. So we might access the SPI flash with:
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sf probe 2:0
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and the eeprom with
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sspi 2:1 32 ef
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These commands simply need to look up the 2nd device in the SPI uclass to
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find the right SPI bus. Then, they look at the children of that bus for the
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right sequence number (0 or 1 in this case).
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Typically the alias method is used for top-level nodes and the 'reg' method
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is used only for buses.
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Device sequence numbers are resolved when a device is probed. Before then
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the sequence number is only a request which may or may not be honoured,
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depending on what other devices have been probed. However the numbering is
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entirely under the control of the board author so a conflict is generally
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an error.
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Bus Drivers
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-----------
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A common use of driver model is to implement a bus, a device which provides
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access to other devices. Example of buses include SPI and I2C. Typically
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the bus provides some sort of transport or translation that makes it
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possible to talk to the devices on the bus.
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Driver model provides a few useful features to help with implementing
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buses. Firstly, a bus can request that its children store some 'parent
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data' which can be used to keep track of child state. Secondly, the bus can
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define methods which are called when a child is probed or removed. This is
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similar to the methods the uclass driver provides.
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Here an explanation of how a bus fits with a uclass may be useful. Consider
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a USB bus with several devices attached to it, each from a different (made
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up) uclass:
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xhci_usb (UCLASS_USB)
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eth (UCLASS_ETHERNET)
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camera (UCLASS_CAMERA)
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flash (UCLASS_FLASH_STORAGE)
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Each of the devices is connected to a different address on the USB bus.
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The bus device wants to store this address and some other information such
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as the bus speed for each device.
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To achieve this, the bus device can use dev->parent_priv in each of its
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three children. This can be auto-allocated if the bus driver has a non-zero
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value for per_child_auto_alloc_size. If not, then the bus device can
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allocate the space itself before the child device is probed.
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Also the bus driver can define the child_pre_probe() and child_post_remove()
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methods to allow it to do some processing before the child is activated or
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after it is deactivated.
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Note that the information that controls this behaviour is in the bus's
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driver, not the child's. In fact it is possible that child has no knowledge
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that it is connected to a bus. The same child device may even be used on two
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different bus types. As an example. the 'flash' device shown above may also
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be connected on a SATA bus or standalone with no bus:
|
|
|
|
xhci_usb (UCLASS_USB)
|
|
flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by USB bus
|
|
|
|
sata (UCLASS_SATA)
|
|
flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by SATA bus
|
|
|
|
flash (UCLASS_FLASH_STORAGE) - no parent data/methods (not on a bus)
|
|
|
|
Above you can see that the driver for xhci_usb/sata controls the child's
|
|
bus methods. In the third example the device is not on a bus, and therefore
|
|
will not have these methods at all. Consider the case where the flash
|
|
device defines child methods. These would be used for *its* children, and
|
|
would be quite separate from the methods defined by the driver for the bus
|
|
that the flash device is connetced to. The act of attaching a device to a
|
|
parent device which is a bus, causes the device to start behaving like a
|
|
bus device, regardless of its own views on the matter.
|
|
|
|
The uclass for the device can also contain data private to that uclass.
|
|
But note that each device on the bus may be a memeber of a different
|
|
uclass, and this data has nothing to do with the child data for each child
|
|
on the bus.
|
|
|
|
|
|
Driver Lifecycle
|
|
----------------
|
|
|
|
Here are the stages that a device goes through in driver model. Note that all
|
|
methods mentioned here are optional - e.g. if there is no probe() method for
|
|
a device then it will not be called. A simple device may have very few
|
|
methods actually defined.
|
|
|
|
1. Bind stage
|
|
|
|
A device and its driver are bound using one of these two methods:
|
|
|
|
- Scan the U_BOOT_DEVICE() definitions. U-Boot It looks up the
|
|
name specified by each, to find the appropriate driver. It then calls
|
|
device_bind() to create a new device and bind' it to its driver. This will
|
|
call the device's bind() method.
|
|
|
|
- Scan through the device tree definitions. U-Boot looks at top-level
|
|
nodes in the the device tree. It looks at the compatible string in each node
|
|
and uses the of_match part of the U_BOOT_DRIVER() structure to find the
|
|
right driver for each node. It then calls device_bind() to bind the
|
|
newly-created device to its driver (thereby creating a device structure).
|
|
This will also call the device's bind() method.
|
|
|
|
At this point all the devices are known, and bound to their drivers. There
|
|
is a 'struct udevice' allocated for all devices. However, nothing has been
|
|
activated (except for the root device). Each bound device that was created
|
|
from a U_BOOT_DEVICE() declaration will hold the platdata pointer specified
|
|
in that declaration. For a bound device created from the device tree,
|
|
platdata will be NULL, but of_offset will be the offset of the device tree
|
|
node that caused the device to be created. The uclass is set correctly for
|
|
the device.
|
|
|
|
The device's bind() method is permitted to perform simple actions, but
|
|
should not scan the device tree node, not initialise hardware, nor set up
|
|
structures or allocate memory. All of these tasks should be left for
|
|
the probe() method.
|
|
|
|
Note that compared to Linux, U-Boot's driver model has a separate step of
|
|
probe/remove which is independent of bind/unbind. This is partly because in
|
|
U-Boot it may be expensive to probe devices and we don't want to do it until
|
|
they are needed, or perhaps until after relocation.
|
|
|
|
2. Activation/probe
|
|
|
|
When a device needs to be used, U-Boot activates it, by following these
|
|
steps (see device_probe()):
|
|
|
|
a. If priv_auto_alloc_size is non-zero, then the device-private space
|
|
is allocated for the device and zeroed. It will be accessible as
|
|
dev->priv. The driver can put anything it likes in there, but should use
|
|
it for run-time information, not platform data (which should be static
|
|
and known before the device is probed).
|
|
|
|
b. If platdata_auto_alloc_size is non-zero, then the platform data space
|
|
is allocated. This is only useful for device tree operation, since
|
|
otherwise you would have to specific the platform data in the
|
|
U_BOOT_DEVICE() declaration. The space is allocated for the device and
|
|
zeroed. It will be accessible as dev->platdata.
|
|
|
|
c. If the device's uclass specifies a non-zero per_device_auto_alloc_size,
|
|
then this space is allocated and zeroed also. It is allocated for and
|
|
stored in the device, but it is uclass data. owned by the uclass driver.
|
|
It is possible for the device to access it.
|
|
|
|
d. If the device's immediate parent specifies a per_child_auto_alloc_size
|
|
then this space is allocated. This is intended for use by the parent
|
|
device to keep track of things related to the child. For example a USB
|
|
flash stick attached to a USB host controller would likely use this
|
|
space. The controller can hold information about the USB state of each
|
|
of its children.
|
|
|
|
e. All parent devices are probed. It is not possible to activate a device
|
|
unless its predecessors (all the way up to the root device) are activated.
|
|
This means (for example) that an I2C driver will require that its bus
|
|
be activated.
|
|
|
|
f. The device's sequence number is assigned, either the requested one
|
|
(assuming no conflicts) or the next available one if there is a conflict
|
|
or nothing particular is requested.
|
|
|
|
g. If the driver provides an ofdata_to_platdata() method, then this is
|
|
called to convert the device tree data into platform data. This should
|
|
do various calls like fdtdec_get_int(gd->fdt_blob, dev->of_offset, ...)
|
|
to access the node and store the resulting information into dev->platdata.
|
|
After this point, the device works the same way whether it was bound
|
|
using a device tree node or U_BOOT_DEVICE() structure. In either case,
|
|
the platform data is now stored in the platdata structure. Typically you
|
|
will use the platdata_auto_alloc_size feature to specify the size of the
|
|
platform data structure, and U-Boot will automatically allocate and zero
|
|
it for you before entry to ofdata_to_platdata(). But if not, you can
|
|
allocate it yourself in ofdata_to_platdata(). Note that it is preferable
|
|
to do all the device tree decoding in ofdata_to_platdata() rather than
|
|
in probe(). (Apart from the ugliness of mixing configuration and run-time
|
|
data, one day it is possible that U-Boot will cache platformat data for
|
|
devices which are regularly de/activated).
|
|
|
|
h. The device's probe() method is called. This should do anything that
|
|
is required by the device to get it going. This could include checking
|
|
that the hardware is actually present, setting up clocks for the
|
|
hardware and setting up hardware registers to initial values. The code
|
|
in probe() can access:
|
|
|
|
- platform data in dev->platdata (for configuration)
|
|
- private data in dev->priv (for run-time state)
|
|
- uclass data in dev->uclass_priv (for things the uclass stores
|
|
about this device)
|
|
|
|
Note: If you don't use priv_auto_alloc_size then you will need to
|
|
allocate the priv space here yourself. The same applies also to
|
|
platdata_auto_alloc_size. Remember to free them in the remove() method.
|
|
|
|
i. The device is marked 'activated'
|
|
|
|
j. The uclass's post_probe() method is called, if one exists. This may
|
|
cause the uclass to do some housekeeping to record the device as
|
|
activated and 'known' by the uclass.
|
|
|
|
3. Running stage
|
|
|
|
The device is now activated and can be used. From now until it is removed
|
|
all of the above structures are accessible. The device appears in the
|
|
uclass's list of devices (so if the device is in UCLASS_GPIO it will appear
|
|
as a device in the GPIO uclass). This is the 'running' state of the device.
|
|
|
|
4. Removal stage
|
|
|
|
When the device is no-longer required, you can call device_remove() to
|
|
remove it. This performs the probe steps in reverse:
|
|
|
|
a. The uclass's pre_remove() method is called, if one exists. This may
|
|
cause the uclass to do some housekeeping to record the device as
|
|
deactivated and no-longer 'known' by the uclass.
|
|
|
|
b. All the device's children are removed. It is not permitted to have
|
|
an active child device with a non-active parent. This means that
|
|
device_remove() is called for all the children recursively at this point.
|
|
|
|
c. The device's remove() method is called. At this stage nothing has been
|
|
deallocated so platform data, private data and the uclass data will all
|
|
still be present. This is where the hardware can be shut down. It is
|
|
intended that the device be completely inactive at this point, For U-Boot
|
|
to be sure that no hardware is running, it should be enough to remove
|
|
all devices.
|
|
|
|
d. The device memory is freed (platform data, private data, uclass data,
|
|
parent data).
|
|
|
|
Note: Because the platform data for a U_BOOT_DEVICE() is defined with a
|
|
static pointer, it is not de-allocated during the remove() method. For
|
|
a device instantiated using the device tree data, the platform data will
|
|
be dynamically allocated, and thus needs to be deallocated during the
|
|
remove() method, either:
|
|
|
|
1. if the platdata_auto_alloc_size is non-zero, the deallocation
|
|
happens automatically within the driver model core; or
|
|
|
|
2. when platdata_auto_alloc_size is 0, both the allocation (in probe()
|
|
or preferably ofdata_to_platdata()) and the deallocation in remove()
|
|
are the responsibility of the driver author.
|
|
|
|
e. The device sequence number is set to -1, meaning that it no longer
|
|
has an allocated sequence. If the device is later reactivated and that
|
|
sequence number is still free, it may well receive the name sequence
|
|
number again. But from this point, the sequence number previously used
|
|
by this device will no longer exist (think of SPI bus 2 being removed
|
|
and bus 2 is no longer available for use).
|
|
|
|
f. The device is marked inactive. Note that it is still bound, so the
|
|
device structure itself is not freed at this point. Should the device be
|
|
activated again, then the cycle starts again at step 2 above.
|
|
|
|
5. Unbind stage
|
|
|
|
The device is unbound. This is the step that actually destroys the device.
|
|
If a parent has children these will be destroyed first. After this point
|
|
the device does not exist and its memory has be deallocated.
|
|
|
|
|
|
Data Structures
|
|
---------------
|
|
|
|
Driver model uses a doubly-linked list as the basic data structure. Some
|
|
nodes have several lists running through them. Creating a more efficient
|
|
data structure might be worthwhile in some rare cases, once we understand
|
|
what the bottlenecks are.
|
|
|
|
|
|
Changes since v1
|
|
----------------
|
|
|
|
For the record, this implementation uses a very similar approach to the
|
|
original patches, but makes at least the following changes:
|
|
|
|
- Tried to aggressively remove boilerplate, so that for most drivers there
|
|
is little or no 'driver model' code to write.
|
|
- Moved some data from code into data structure - e.g. store a pointer to
|
|
the driver operations structure in the driver, rather than passing it
|
|
to the driver bind function.
|
|
- Rename some structures to make them more similar to Linux (struct udevice
|
|
instead of struct instance, struct platdata, etc.)
|
|
- Change the name 'core' to 'uclass', meaning U-Boot class. It seems that
|
|
this concept relates to a class of drivers (or a subsystem). We shouldn't
|
|
use 'class' since it is a C++ reserved word, so U-Boot class (uclass) seems
|
|
better than 'core'.
|
|
- Remove 'struct driver_instance' and just use a single 'struct udevice'.
|
|
This removes a level of indirection that doesn't seem necessary.
|
|
- Built in device tree support, to avoid the need for platdata
|
|
- Removed the concept of driver relocation, and just make it possible for
|
|
the new driver (created after relocation) to access the old driver data.
|
|
I feel that relocation is a very special case and will only apply to a few
|
|
drivers, many of which can/will just re-init anyway. So the overhead of
|
|
dealing with this might not be worth it.
|
|
- Implemented a GPIO system, trying to keep it simple
|
|
|
|
|
|
Pre-Relocation Support
|
|
----------------------
|
|
|
|
For pre-relocation we simply call the driver model init function. Only
|
|
drivers marked with DM_FLAG_PRE_RELOC or the device tree
|
|
'u-boot,dm-pre-reloc' flag are initialised prior to relocation. This helps
|
|
to reduce the driver model overhead.
|
|
|
|
Then post relocation we throw that away and re-init driver model again.
|
|
For drivers which require some sort of continuity between pre- and
|
|
post-relocation devices, we can provide access to the pre-relocation
|
|
device pointers, but this is not currently implemented (the root device
|
|
pointer is saved but not made available through the driver model API).
|
|
|
|
|
|
SPL Support
|
|
-----------
|
|
|
|
Driver model can operate in SPL. Its efficient implementation and small code
|
|
size provide for a small overhead which is acceptable for all but the most
|
|
constrained systems.
|
|
|
|
To enable driver model in SPL, define CONFIG_SPL_DM. You might want to
|
|
consider the following option also. See the main README for more details.
|
|
|
|
- CONFIG_SYS_MALLOC_SIMPLE
|
|
- CONFIG_DM_WARN
|
|
- CONFIG_DM_DEVICE_REMOVE
|
|
- CONFIG_DM_STDIO
|
|
|
|
|
|
Enabling Driver Model
|
|
---------------------
|
|
|
|
Driver model is being brought into U-Boot gradually. As each subsystems gets
|
|
support, a uclass is created and a CONFIG to enable use of driver model for
|
|
that subsystem.
|
|
|
|
For example CONFIG_DM_SERIAL enables driver model for serial. With that
|
|
defined, the old serial support is not enabled, and your serial driver must
|
|
conform to driver model. With that undefined, the old serial support is
|
|
enabled and driver model is not available for serial. This means that when
|
|
you convert a driver, you must either convert all its boards, or provide for
|
|
the driver to be compiled both with and without driver model (generally this
|
|
is not very hard).
|
|
|
|
See the main README for full details of the available driver model CONFIG
|
|
options.
|
|
|
|
|
|
Things to punt for later
|
|
------------------------
|
|
|
|
Uclasses are statically numbered at compile time. It would be possible to
|
|
change this to dynamic numbering, but then we would require some sort of
|
|
lookup service, perhaps searching by name. This is slightly less efficient
|
|
so has been left out for now. One small advantage of dynamic numbering might
|
|
be fewer merge conflicts in uclass-id.h.
|
|
|
|
|
|
Simon Glass
|
|
sjg@chromium.org
|
|
April 2013
|
|
Updated 7-May-13
|
|
Updated 14-Jun-13
|
|
Updated 18-Oct-13
|
|
Updated 5-Nov-13
|