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

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Date:   Tue, 11 Jul 2017 09:34:34 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     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>,
        Grygorii Strashko <grygorii.strashko@...com>
Subject: Re: [GIT pull] irq updates for 4.13

* Thomas Gleixner <tglx@...utronix.de> [170711 09:20]:
> On Tue, 11 Jul 2017, Linus Torvalds wrote:
> 
> > On Tue, Jul 11, 2017 at 7:41 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > >
> > > Ah. Now that makes sense.
> > >
> > > Unpatched the ordering is:
> > >
> > >           chip_bus_lock(desc);
> > >           irq_request_resources(desc);
> > 
> > I *looked* at that ordering and then went "Naah, that makes no sense".
> > 
> > But if that's the only issue, how about we just re-order those things
> > - we still don't need to move the irq_request_resources() into the
> > spinlock, we just move it to below the chip_bus_lock().
> > 
> > IOW, something like the (COMPLETELY UNTEESTED!) attached patch.
> > 
> > This assumes that the chip_bus_lock() thing is still ok for the RT
> > case, but it looks like it might be: the only other one I looked at
> > (apart from the gpio-omap one) used a mutex.
> 
> I looked through all of them and the only special case is gpio-omap.
> 
> What I do not understand here is that we have already power management
> around all of that.
> 
>        irq_chip_pm_get(&desc->irq_data);
>        ...
>        chip_bus_lock(desc);
>        ...
>        chip_bus_unlock_sync(desc);
>        ...
>        irq_chip_pm_put(&desc->irq_data);
> 
> So why is that not sufficient and needs extra magic in that GPIO driver?

Yeah it seems we should eventually be able to use irq_chip_pm_get()
like Grygorii just explained.

But aren't we currently calling chip functions with irq_request_resources()
outside the chip_bus_lock() too in addition to the gpio-omap runtime PM
issue? It seems that the patch from Linus fixes that, no?

Regards,

Tony