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

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Date:	Tue, 17 Nov 2015 11:57:12 +0000
From:	Jon Hunter <jonathanh@...dia.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Kevin Hilman <khilman@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [RFC PATCH 1/2] genirq: Add runtime resume/suspend support for
 IRQ chips

Hi Geert,

On 16/11/15 10:48, Geert Uytterhoeven wrote:
> On Mon, Nov 16, 2015 at 11:34 AM, Jon Hunter <jonathanh@...dia.com> wrote:

[snip]

>>> Handling it automatically needs more bookkeeping than a simple reference
>>> count.
>>
>> So what would you suggest? Adding a pm_runtime_register_irq() API that
>> would register an IRQ with the device that you want RPM to handle? Not
>> sure if there is a better/easier way to handle this.
> 
> The irqchip needs to keep track how many times request_irq() has been
> called, cfr. your suggestion above.
> 
> On the other side, the system needs to keep track how many times request_irq()
> has been called for each irqchip, so it can subtract those numbers from the
> irqchip's counters during suspend of the device, and re-add them during resume.
> So we need at least a "struct device *" parameter for request_irq().
> devm_request_irq() already has that, but not all drivers use that.

Yes that would make sense. However, I am wondering if the
syscore suspend/resume operators could be used here to do something
like ...

	pm_runtime_disable(dev);
	if (!pm_runtime_status_suspended(dev))
		chip->irq_runtime_suspend(data);

> However, I think this should be looked at into the context of "[RFD]
> Functional dependencies between devices".
> https://lwn.net/Articles/662205/
> https://lkml.org/lkml/2015/10/27/388
> 
> There can be other dependencies than interrupts between devices.
> All functions using dependencies need a "struct device *" parameter to
> record information.

Yes I like the sound of that. That would be ideal. However, I am
guessing that that is a way off at the moment ...

Cheers
Jon
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