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https://github.com/brain-hackers/u-boot-brain
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b725dc458f
While I2C supports multi-master buses this is difficult to get right. The implementation on the master side in software is quite complex. Clock-stretching and the arbitrary time that an I2C transaction can take make it difficult to share the bus fairly in the face of high traffic. When one or more masters can be reset independently part-way through a transaction it is hard to know the state of the bus. This driver provides a scheme based on two 'claim' GPIOs, one driven by the AP (Application Processor, meaning the main CPU) and one driven by the EC (Embedded Controller, a small CPU aimed at handling system tasks). With these they can communicate and reliably share the bus. This scheme has minimal overhead and involves very little code. It is used on snow to permit the EC and the AP to share access to the main system PMIC and battery. The scheme can survive reboots by either side without difficulty. This scheme has been tested in the field with millions of devices. Since U-Boot runs on the AP, the terminology used is 'our' claim GPIO, meaning the AP's, and 'their' claim GPIO, meaning the EC's. This terminology is used by the device tree bindings in Linux also. Signed-off-by: Simon Glass <sjg@chromium.org>
18 lines
665 B
Plaintext
18 lines
665 B
Plaintext
config I2C_MUX
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bool "Suport I2C multiplexers"
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depends on DM_I2C
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help
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This enables I2C buses to be multiplexed, so that you can select
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one of several buses using some sort of control mechanism. The
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bus select is handled automatically when that bus is accessed,
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using a suitable I2C MUX driver.
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config I2C_ARB_GPIO_CHALLENGE
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bool "GPIO-based I2C arbitration"
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depends on I2C_MUX
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help
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If you say yes to this option, support will be included for an
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I2C multimaster arbitration scheme using GPIOs and a challenge &
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response mechanism where masters have to claim the bus by asserting
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a GPIO.
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