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Andy Shevchenko fbe80b3ee9 staging: fbtft: Rectify GPIO handling 
[ Upstream commit ec03c2104365ead0a33627c05e685093eed3eaef ]

The infamous commit c440eee1a7 ("Staging: staging: fbtft: Switch to
the GPIO descriptor interface") broke GPIO handling completely.
It has already four commits to rectify and it seems not enough.
In order to fix the mess here we:

  1) Set default to "inactive" for all requested pins

  2) Fix CS#, RD#, and WR# pins polarity since it's active low
     and GPIO descriptor interface takes it into consideration
     from the Device Tree or ACPI

  3) Consolidate chip activation (CS# assertion) under default
     ->reset() callback

To summarize the expectations about polarity for GPIOs:

   RD#			Low
   WR#			Low
   CS#			Low
   RESET#		Low
   DC or RS		High
   RW			High
   Data	0 .. 15		High

See also Adafruit learning course [1] for the example of the schematics.

While at it, drop unneeded NULL checks, since GPIO API is tolerant to that.

[1]: https://learn.adafruit.com/adafruit-2-8-and-3-2-color-tft-touchscreen-breakout-v2/downloads

Fixes: 92e3e88488 ("Staging: fbtft: Fix GPIO handling")
Fixes: b918d1c270 ("Staging: fbtft: Fix reset assertion when using gpio descriptor")
Fixes: dbc4f989c8 ("Staging: fbtft: Fix probing of gpio descriptor")
Fixes: c440eee1a7 ("Staging: fbtft: Switch to the gpio descriptor interface")
Cc: Jan Sebastian Götte <linux@jaseg.net>
Cc: Nishad Kamdar <nishadkamdar@gmail.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210503172114.27891-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2021-07-14 16:53:36 +02:00
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Kconfig
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Makefile
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README
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TODO
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fbtft-bus.c
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fbtft-io.c
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fbtft-sysfs.c
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fbtft.h
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internal.h
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README 

  FBTFT
=========

Linux Framebuffer drivers for small TFT LCD display modules.
The module 'fbtft' makes writing drivers for some of these displays very easy.

Development is done on a Raspberry Pi running the Raspbian "wheezy" distribution.

INSTALLATION
  Download kernel sources

  From Linux 3.15
    cd drivers/video/fbdev/fbtft
    git clone https://github.com/notro/fbtft.git

    Add to drivers/video/fbdev/Kconfig:   source "drivers/video/fbdev/fbtft/Kconfig"
    Add to drivers/video/fbdev/Makefile:  obj-y += fbtft/

  Before Linux 3.15
    cd drivers/video
    git clone https://github.com/notro/fbtft.git

    Add to drivers/video/Kconfig:   source "drivers/video/fbtft/Kconfig"
    Add to drivers/video/Makefile:  obj-y += fbtft/

  Enable driver(s) in menuconfig and build the kernel


See wiki for more information: https://github.com/notro/fbtft/wiki


Source: https://github.com/notro/fbtft/