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

Tomasz Nowicki
2014-08-18T09:06:49Z

On 08.08.2014 14:36, 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.
>
> It seems a bit confusing for me: why do you have to extract
> a number from one file and then insert the same magic number
> somewhere else?

Good point! Available GPIO event pins should be listed as debugfs node,
then user would write e.g. 1 to one particular. Sounds simpler.

Regards,
Tomasz Nowicki