linux-kernel - Re: [RFC PATCH 1/2] genirq: Add runtime resume/suspend support for IRQ chips

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Date:	Thu, 12 Nov 2015 15:38:23 +0000
From:	Jon Hunter <jonathanh@...dia.com>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kevin Hilman <khilman@...nel.org>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	LKML <linux-kernel@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>,
	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [RFC PATCH 1/2] genirq: Add runtime resume/suspend support for
 IRQ chips


On 12/11/15 14:37, Lars-Peter Clausen wrote:
> On 11/12/2015 03:02 PM, Jon Hunter wrote:
> [...]
>>>>> One easy way out might be to always call pm_get/pm_but from
>>>>> bus_lock,/bus_unlock. This way the chip is guaranteed to be powered up when
>>>>> accessed happens. In addition pm_get is called when the IRQ is request and
>>>>> pm_put is called when the IRQ is release, this is to ensure the chip stays
>>>>> powered when it is actively monitoring the IRQ lines.
>>>>
>>>> Yes I had thought about that, but it is not quite that easy, because in
>>>> the case of request_irq() you don't want to pm_put() after the
>>>> bus_unlock(). However, the bus_lock/unlock() are good indicators of
>>>> different paths.
>>>
>>> You'd call pm_get() twice in request_irq() once from bus_lock() and once
>>> independently, that way you still have a reference even after the bus_unlock().
>>
>> Yes that is a possibility. However, there are places such as
>> show_interrupts() (kernel/irq/proc.c) and irq_gc_suspend() that do not
>> call bus_lock/unlock() which would need to be handled for PM. May be
>> these should also call bus_lock() as well?
> 
> show_interrupts() only accesses software state, not hardware state, or does it?

Good point. Today there only appears to be one user:

arch/powerpc/sysdev/fsl_msi.c:	.irq_print_chip = fsl_msi_print_chip,

This one is purely software. However, it would be easy to handle the
show_interrupts case if needed.

> suspend/resume is a bit tricky. It's kind of driver specific if it needs to
> actually access the hardware or whether the state is already shadowed in
> software. Maybe we can make this an exception for now and let drivers handle
> this on their own.

Yes I would agree with you on that.

Cheers
Jon

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