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

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Message-ID: <53F1C226.5090107@linaro.org>
Date:	Mon, 18 Aug 2014 11:06:46 +0200
From:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
CC:	Alexandre Courbot <gnurou@...il.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [RFC] ACPI: Add GPIO-signaled event simulator.

On 08.08.2014 14:36, Linus Walleij wrote:
> On Thu, Jul 24, 2014 at 5:51 PM, Tomasz Nowicki
> <tomasz.nowicki@...aro.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
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