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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
zero-sugar-mainline-defconfig
Linus Walleij 2020-12-04 09:35:33 +01:00
parent c47d9e1b73
commit dd0fa81143
1 changed files with 36 additions and 0 deletions
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36
drivers/gpio/TODO
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@ -142,3 +142,39 @@ use of the global GPIO numbers. Once the above is complete, it may
make sense to simply join the subsystems into one and make pin
multiplexing, pin configuration, GPIO, etc selectable options in one
and the same pin control and GPIO subsystem.
Debugfs in place of sysfs
The old sysfs code that enables simple uses of GPIOs from the
command line is still popular despite the existance of the proper
character device. The reason is that it is simple to use on
root filesystems where you only have a minimal set of tools such
as "cat", "echo" etc.
The old sysfs still need to be strongly deprecated and removed
as it relies on the global GPIO numberspace that assume a strict
order of global GPIO numbers that do not change between boots
and is independent of probe order.
To solve this and provide an ABI that people can use for hacks
and development, implement a debugfs interface to manipulate
GPIO lines that can do everything that sysfs can do today: one
directory per gpiochip and one file entry per line:
/sys/kernel/debug/gpiochip/gpiochip0
/sys/kernel/debug/gpiochip/gpiochip0/gpio0
/sys/kernel/debug/gpiochip/gpiochip0/gpio1
/sys/kernel/debug/gpiochip/gpiochip0/gpio2
/sys/kernel/debug/gpiochip/gpiochip0/gpio3
...
/sys/kernel/debug/gpiochip/gpiochip1
/sys/kernel/debug/gpiochip/gpiochip1/gpio0
/sys/kernel/debug/gpiochip/gpiochip1/gpio1
...
The exact files and design of the debugfs interface can be
discussed but the idea is to provide a low-level access point
for debugging and hacking and to expose all lines without the
need of any exporting. Also provide ample ammunition to shoot
oneself in the foot, because this is debugfs after all.