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kernel
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linux
gpio: Add TODO item for debugfs interface
The idea to create a debugfs to replace the aging and
dangerous sysfs ABI for hacking and tinkering came up
on the list.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201204083533.65830-1-linus.walleij@linaro.org
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drivers/gpio/TODO
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drivers/gpio/TODO
···
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make sense to simply join the subsystems into one and make pin
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multiplexing, pin configuration, GPIO, etc selectable options in one
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and the same pin control and GPIO subsystem.
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Debugfs in place of sysfs
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The old sysfs code that enables simple uses of GPIOs from the
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command line is still popular despite the existance of the proper
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character device. The reason is that it is simple to use on
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root filesystems where you only have a minimal set of tools such
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as "cat", "echo" etc.
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The old sysfs still need to be strongly deprecated and removed
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as it relies on the global GPIO numberspace that assume a strict
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order of global GPIO numbers that do not change between boots
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and is independent of probe order.
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To solve this and provide an ABI that people can use for hacks
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and development, implement a debugfs interface to manipulate
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GPIO lines that can do everything that sysfs can do today: one
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directory per gpiochip and one file entry per line:
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/sys/kernel/debug/gpiochip/gpiochip0
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/sys/kernel/debug/gpiochip/gpiochip0/gpio0
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/sys/kernel/debug/gpiochip/gpiochip0/gpio1
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/sys/kernel/debug/gpiochip/gpiochip0/gpio2
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/sys/kernel/debug/gpiochip/gpiochip0/gpio3
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...
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/sys/kernel/debug/gpiochip/gpiochip1
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/sys/kernel/debug/gpiochip/gpiochip1/gpio0
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/sys/kernel/debug/gpiochip/gpiochip1/gpio1
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...
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The exact files and design of the debugfs interface can be
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discussed but the idea is to provide a low-level access point
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for debugging and hacking and to expose all lines without the
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need of any exporting. Also provide ample ammunition to shoot
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oneself in the foot, because this is debugfs after all.