linux-kernel - Re: [PATCH for 4.12] Revert "pinctrl: rockchip: avoid hardirq-unsafe functions in irq

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Date:   Tue, 27 Jun 2017 18:35:11 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Heiko Stübner <heiko@...ech.de>
cc:     Brian Norris <briannorris@...omium.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-rockchip@...ts.infradead.org,
        Julia Cartwright <julia@...com>,
        LKML <linux-kernel@...r.kernel.org>, linux-gpio@...r.kernel.org,
        John Keeping <john@...anate.com>, linux-pm@...r.kernel.org,
        Doug Anderson <dianders@...omium.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Lindgren <tony@...mide.com>,
        "David.Wu" <david.wu@...k-chips.com>,
        '黄涛' <huangtao@...k-chips.com>
Subject: Re: [PATCH for 4.12] Revert "pinctrl: rockchip: avoid hardirq-unsafe
 functions in irq_chip"

On Tue, 27 Jun 2017, Heiko Stübner wrote:
> Am Dienstag, 27. Juni 2017, 15:01:32 CEST schrieb Thomas Gleixner:
> > The only irq chip function which uses the regmap magic is the
> > irq_set_type() callback. Now, I have a hard time to understand (though I'm
> > no regmap/pinctrl expert) why that regmap stuff needs to be called in the
> > first place. The level and the polarity are programmed via:
> > 
> >         writel_relaxed(level, gc->reg_base + GPIO_INTTYPE_LEVEL);
> >         writel_relaxed(polarity, gc->reg_base + GPIO_INT_POLARITY);
> > 
> > Why needs the regmap machinery to be invoked there? The GPIO is already
> > muxed and configured as interrupt, otherwise none of the irq functions
> > could be invoked. Hmm?
> 
> That is a safeguard against the pinmux not being set as "gpio" but some other 
> function, if the irq is requested directly without going through the gpio API. 
> 
> But looking at struct irq_chip and also other pinctrl drivers again, it seems
> the new [0] irq_request_resources might be the way saner place for this.
> Especially as it also prevents the mux-setting from being called more than 
> once.

That'll fail on RT as well because irq_request_resources() is called with
irq_desc->lock held and interrupts disabled.

irq_request_resources() can probably be called without holding desc->lock,
though we need some form of protection against concurrent irq
requests/free. I'll have look into that.

Thanks,

	tglx