Re: [RFC] ACPI: Add GPIO-signaled event simulator.

Tomasz Nowicki
2014-08-18T09:28:09Z

On 12.08.2014 12:01, Mika Westerberg wrote:
> On Fri, Aug 08, 2014 at 02:36:02PM +0200, Linus Walleij wrote:
>> On Thu, Jul 24, 2014 at 5:51 PM, Tomasz Nowicki
>> <tomasz.nowicki@linaro.org> wrote:
>>
>>> GPIO signaled events is quite new thing in Linux kernel.
>>> AFAIK, there are not many board which can take advantage of it.
>>> However, GPIO events are very useful feature during work on ACPI
>>> subsystems.
>>
>> Overall this seems like a pretty nice debug feature.
>>
>>> This commit emulates GPIO h/w behaviour and consists on read/write
>>> operation to debugfs file. GPIO device instance is still required in DSDT
>>> table along with _AEI resources and event methods.
>>>
>>> Reading from file provides pin to GPIO device map e.g. :
>>> $ cat /sys/kernel/debug/acpi/gpio_event
>>> GPIO device name: /__SB.GPI0
>>> Available GPIO pin map:
>>> /__SB.GPI0 <-> pin 0x100
>>>
>>> Based on that, user can trigger method corresponding to device pin number:
>>> $ echo "/__SB.GPI0 0x100" > /sys/kernel/debug/acpi/gpio_event
>>
>> I need input from Rafael and Mika as to whether this is a
>> good interface.
>
> Maybe it would make sense to move this into drivers/gpio/gpiolib-acpi.c
> and hide it behind some Kconfig entry?
>
> Since you already need to have DSDT/SSDT table for this to provide the
> GPIO device, _AEI and the event methods, I would rather make it so that
> acpi_gpiochip_request_interrupt() will add debugfs entry for each GPIO
> it finds in _AEI, like:
>
> /sys/kernel/debug/acpi/events/<GPIO DEVICE>/n
>
> And you could trigger it by writing '1' or something like that to that
> file.
>

Thanks for comments. The idea of available gpio events list under
/sys/kernel/debug/acpi/events/<GPIO DEVICE>/n is worth adding.

However, acpi_gpiochip_request_interrupt() would be called if we would
have real GPIO H/W and related driver. Initial idea of this patch was to
avoid that restriction. So there are two cases:
1. If we have GPIO chip, it is already described in DSDT/SSDT and using
this patch, user could trigger events by software too.
2. None of GPIO chip, so we need to add GPIO/_AEI etc. descrition to
DSDT/SSDT and pretend we have GPIO chip on board.

Regards,
Tomasz Nowicki