linux-kernel - Re: [PATCH] gpio: zynq: Implement irq_(request|release)

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Message-ID: <562FBA60.70002@ti.com>
Date:	Tue, 27 Oct 2015 19:54:40 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	John Linn <linnj@...inx.com>
Subject: Re: [PATCH] gpio: zynq: Implement irq_(request|release)_resources

On 10/27/2015 06:23 PM, Linus Walleij wrote:
> On Tue, Oct 27, 2015 at 5:18 PM, Grygorii Strashko
> <grygorii.strashko@...com> wrote:
>> On 10/27/2015 05:53 PM, Linus Walleij wrote:
>>>
>>> On Fri, Oct 23, 2015 at 3:36 PM, Soren Brinkmann
>>> <soren.brinkmann@...inx.com> wrote:
>>>
>>>> The driver uses runtime PM to leverage low power techniques. For
>>>> use-cases using GPIO as interrupt the device needs to be in an
>>>> appropriate state.
>>>>
>>>> Reported-by: John Linn <linnj@...inx.com>
>>>> Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
>>>> Tested-by: John Linn <linnj@...inx.com>
>>>
>>>
>>> As pointed out by Grygorii in
>>> commit aca82d1cbb49af34b69ecd4571a0fe48ad9247c1:
>>>
>>>       The PM runtime API can't be used in atomic contex on -RT even if
>>>       it's configured as irqsafe. As result, below error report can
>>>       be seen when PM runtime API called from IRQ chip's callbacks
>>>       irq_startup/irq_shutdown/irq_set_type, because they are
>>>       protected by RAW spinlock:
>>> (...)
>>>       The IRQ chip interface defines only two callbacks which are executed
>>> in
>>>       non-atomic contex - irq_bus_lock/irq_bus_sync_unlock, so lets move
>>>       PM runtime calls there.
>>>
>>> I.e. these calls are atomic context and it's just luck that it works
>>> and this is fragile.
>>>
>>> Can you please check if you can move it to
>>> irq_bus_lock()/irq_sync_unlock()
>>> like Grygorii does?
>>>
>>
>> This patch rises the question not only about PM runtime, but also
>> about gpiochip_irq_reqres()/gpiochip_irq_relres().
> 
> Do you mean that these functions contain calls to non-atomic
> functions?
> 

Oh. No, I have to be more specific :(
if GPIOx driver defines custom .irq_(request|release)_resources() callbacks
they will *overwrite* standard GPIOirqchip callbacks.
(commit: 8b67a1f "gpio: don't override irq_*_resources() callbacks")

As result, such GPIOx driver should *re-implement* the same functionality in
its .irq_(request|release)_resources() callbacks as implemented in
gpiochip_irq_reqres()/gpiochip_irq_relres().

> I mainly reacted to this because it was pm_* calls, that you
> mentioned explicitly in your patch.
> 
-- 
regards,
-grygorii
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