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

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Message-ID: <20140812100111.GV1657@lahna.fi.intel.com>
Date:	Tue, 12 Aug 2014 13:01:11 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	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 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@...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.

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.
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