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

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Date:	Mon, 16 Nov 2015 10:34:29 +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>
Subject: Re: [RFC PATCH 1/2] genirq: Add runtime resume/suspend support for
 IRQ chips


On 16/11/15 09:49, Geert Uytterhoeven wrote:
> On Mon, Nov 16, 2015 at 10:46 AM, Jon Hunter <jonathanh@...dia.com> wrote:
>> On 13/11/15 20:01, Thomas Gleixner wrote:
>>> On Fri, 13 Nov 2015, Jon Hunter wrote:
>>>> On 12/11/15 23:20, Kevin Hilman wrote:
>>>>> If all the RPM devices in the domain go idle, it will be powered off
>>>>> independently of the status of the irqchip because the irqchip isn't
>>>>> using RPM.
>>>>
>>>> That's dependent on how the irqchip uses these helpers. If these helpers
>>>> invoke RPM then that will not be the case.
>>>
>>> You need a very proper description of how that domain is working. If
>>> all devices are idle, it's not necessary correct to power down the
>>> irqchip as is might serve other devices as well.
>>
>> Agreed. The irqchip should only be powered down if there are no
>> interrupts in-use/requested. Runtime-pm will keep a reference count for
>> all requested IRQs.
> 
> That means the irqchip won't be powered down automatically when the
> last user is powered down, unless all users release their irqs during
> suspend.

Right.

> 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.

Cheers
Jon



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