linux-kernel - Re: [RFC] gpio/omap: auto-setup a GPIO when used as an IRQ

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Date:	Tue, 24 Sep 2013 09:54:54 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Sricharan R <r.sricharan@...com>
CC:	Tony Lindgren <tony@...mide.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	Grant Likely <grant.likely@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Kumar Gala <galak@...eaurora.org>,
	Pawel Moll <pawel.moll@....com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Enric Balletbo i Serra <eballetbo@...il.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Balaji T K <balajitk@...com>,
	Jon Hunter <jgchunter@...il.com>, linux-gpio@...r.kernel.org,
	linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] gpio/omap: auto-setup a GPIO when used as an IRQ

On 09/24/2013 09:39 AM, Sricharan R wrote:
> Hi,
> On Monday 23 September 2013 10:37 PM, Tony Lindgren wrote:
>> * Javier Martinez Canillas <javier.martinez@...labora.co.uk> [130923 10:09]:
>>> On 09/23/2013 06:45 PM, Tony Lindgren wrote:
>>>> Hmm does this still work for legacy platform data based
>>>> drivers that are doing gpio_request() first?
>>>>
>>> Yes it still work when booting using board files. I tested on my OMAP3 board and
>>> it worked in both DT and legacy booting mode.
>> OK great.
>>  
>>>> And what's the path for clearing things for PM when free_irq()
>>>> gets called? It seems that this would leave the GPIO bank
>>>> enabled causing a PM regression?
>>>>
>>> Indeed, I did set bank->mod_usage |= 1 << offset so the bank is enabled if the
>>> device goes to suspended and then resumed but I completely forget about the
>>> clearing path when the IRQ is freed.
>>>
>>> Which makes me think that we should probably maintain two usage variables, one
>>> for GPIO and another one for IRQ and check both of them on the suspend/resume pm
>>> functions.
>> Yes that it seems that they should be treated separately.
>  To understand, why cant the flag be cleared in gpio_irq_shutdown ?

Hi Sricharan,

Without this patch today drivers do this:

gpio_request(gpio, "foo IRQ"); // bank->mod_usage |= 1 << offset
gpio_direction_input(gpio);

and then request a IRQ with:

irq = gpio_to_irq(gpio);
request_irq(irq, ...);

later on its cleanup path:

free_irq(irq, dev);
gpio_free(gpio) // bank->mod_usage &= ~(1 << offset);

So if you clear the flag on gpio_irq_shutdown then bank module won't be enabled
after a suspend making drivers using the GPIO after freeing the IRQ to fail.

So the idea is to have something like this:

a) Drivers that request both the GPIO and IRQ

gpio_request(gpio, "foo IRQ"); // bank->mod_usage |= 1 << offset
gpio_direction_input(gpio);

irq = gpio_to_irq(gpio);
request_irq(irq, ...); // bank->irq_usage |= 1 << offset

free_irq(irq, dev); // bank->irq_usage &= ~(1 << offset);
gpio_free(gpio) // bank->mod_usage &= ~(1 << offset);

b) Drivers that just request the IRQ:

irq = gpio_to_irq(gpio);
request_irq(irq, ...); // bank->irq_usage |= 1 << offset
free_irq(irq, dev); // bank->irq_usage &= ~(1 << offset);

So irq_usage or mod_usage is set means that the bank has to be enabled and if
both are not set means that the bank module can be disabled.

> 
> Regards,
>  Sricharan
> 

Best regards,
Javier
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