linux-kernel - Re: [GIT pull] irq updates for 4.13

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Date:   Wed, 12 Jul 2017 10:00:55 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Tony Lindgren <tony@...mide.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Pavel Machek <pavel@....cz>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [GIT pull] irq updates for 4.13

Hi Grygorii,

On Tue, Jul 11, 2017 at 5:39 PM, Grygorii Strashko
<grygorii.strashko@...com> wrote:
> On 07/11/2017 09:41 AM, Thomas Gleixner wrote:
>> On Tue, 11 Jul 2017, Tony Lindgren wrote:
>>> * Thomas Gleixner <tglx@...utronix.de> [170711 02:48]:
>>> And "external abort on non-linefetch" means something is not clocked
>>> in this case. The following alone makes things boot for me again, but I don't
>>> quite follow what has now changed with the ordering.. Thomas, any ideas?
>>
>> Ah. Now that makes sense.
>>
>> Unpatched the ordering is:
>>
>>         chip_bus_lock(desc);
>>         irq_request_resources(desc);
>>
>> Now the offending change reordered the calls. OMAP gpio has:
>>
>>      omap_gpio_irq_bus_lock()
>>         pm_runtime_get_sync(bank->chip.parent);
>>
>> So that at least explains the error. So that omap gpio irq chip (ab)uses
>> the bus_lock() callback to do runtime power management. Sigh, I did not
>> expect that. Let me have a deeper look if that's OMAP only or whether this
>> happens in other places as well.
>
> It was the only one way to power on GPIO bank when the first GPIO IRQ is requested,
> as all other irqchip callbacks are under raw_lock while pm_runtime uses spinlock, as
> result on -RT it was not possible to use PM runtime in other irqchip callbacks.
>
> Now, I think, It might be possible to use irq_chip_pm_get(), but there is one problem -
> OMAP Power management platform code can call omap2_gpio_prepare_for_idle()/omap2_gpio_resume_after_idle()
> which expected to disable GPIO banks using PM runtime and current driver implementation
> expect to have PM runtime usage_count = 1.
>
> Tony, Potentially we can use pm_runtime_force_suspend()/resume() there, but they are not compatible with
> irqoff context (CPUIdle late stages).
>
> In other words, below patch should fix this issue, but will break CPUIdle on OMAP :(
>
> --
> From dfca1c806f03ad6bdd72b634d71c96d39bda2046 Mon Sep 17 00:00:00 2001
> From: Grygorii Strashko <grygorii.strashko@...com>
> Date: Tue, 11 Jul 2017 10:36:23 -0500
> Subject: [PATCH] gpio: omap: switch to use irq_chip_pm_get/put()
>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>

That looks similar to how gpio-rcar was fixed, which used to do the
same trick in its bus_lock() callbacks.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds