linux-kernel - Re: [PATCH] clk: Fix race conditions between clk_set_parent() and clk

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Date:	Tue, 15 May 2012 23:00:50 -0700
From:	"Turquette, Mike" <mturquette@...com>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	Arnd Bergman <arnd.bergmann@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
	Paul Walmsley <paul@...an.com>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-arm-msm@...r.kernel.org,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Richard Zhao <richard.zhao@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Deepak Saxena <dsaxena@...aro.org>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Jamie Iles <jamie@...ieiles.com>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shawn Guo <shawn.guo@...escale.com>
Subject: Re: [PATCH] clk: Fix race conditions between clk_set_parent() and clk_enable()

On Fri, May 11, 2012 at 9:59 PM, Saravana Kannan <skannan@...eaurora.org> wrote:
> Since clocks with CLK_SET_PARENT_GATE flag only allow clk_set_parent() on
> unprepared clocks and calling clk_enable() on an unprepared clock would be
> violating the clock API usage model, allow set_parent() ops to be sleepable
> for clocks which have the CLK_SET_PARENT_GATE flag. Putting it another way,
> if a clock's parent can't be switched without sleeping, then by definition
> the parent can't be switched while it's prepared (CLK_SET_PARENT_GATE).
>
...
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index e5d5dc1..09b9112 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1059,7 +1059,7 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent)
>  {
>        struct clk *old_parent;
>        unsigned long flags;
> -       int ret = -EINVAL;
> +       int ret;
>        u8 i;
>
>        old_parent = clk->parent;
> @@ -1083,7 +1083,13 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent)
>        if (i == clk->num_parents) {
>                pr_debug("%s: clock %s is not a possible parent of clock %s\n",
>                                __func__, parent->name, clk->name);
> -               goto out;
> +               return -EINVAL;
> +       }
> +
> +       if (clk->flags & CLK_SET_PARENT_GATE) {
> +               ret = clk->ops->set_parent(clk->hw, i);
> +               clk->parent = parent;
> +               return ret;
>        }
>
>        /* migrate prepare and enable */

The above hunk is a good change since it fixes a bug where we
prepare/enable the parent clocks around the .set_parent callback, even
when CLK_SET_PARENT_GATE is set.  It should be a separate patch.

Thanks,
Mike
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