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Date: Thu, 21 Jan 2016 13:40:58 +0100
Message-ID: <CAPDyKFrqQO6Mh7ew5YTW011a11LmFW7c+cZpAKmY8tovxjGmOw@mail.gmail.com>
Subject: Re: [RFC PATCH V2 3/8] genirq: Add runtime power management support
 for IRQ chips
From: Ulf Hansson <ulf.hansson@linaro.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Jon Hunter <jonathanh@nvidia.com>, Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Jiang Liu <jiang.liu@linux.intel.com>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Kevin Hilman <khilman@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        Soren Brinkmann <soren.brinkmann@xilinx.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>
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[...]

>> > I don't think using __free_irq() is the correct place to decrease the
>> > runtime PM usage count. It will keep the irqchip runtime resumed even
>> > if there are no irqs enabled for it.
>> >
>> > Instead I would rather allow the irqchip to be runtime suspended, when
>> > there are no irqs enabled on it.
>
> Which is a no no, as you might lose interrupts that way. We disable interrupts
> lazy, i.e. we do not mask them. So no, you cannot do that from
> enable/disable_irq().

Thanks for the input!

My main point around the approach suggested in $subject patch, is that
I don't think it's *enough* fine grained.

>>From a runtime PM perspective, we should allow the irqchip to enter a
low power state when there are no IRQs enabled for it.

As enable|disable_irq() isn't the place to do runtime PM reference
counting from, perhaps there is another option? Maybe the irqchip
driver itself is better suited to take these decisions?

[...]

Kind regards
Uffe