linux-kernel - Re: [PATCH v2 1/4] [RFC] clk: new locking scheme for reentrancy

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Date:	Tue, 4 Sep 2012 22:25:05 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linus.walleij@...aro.org,
	rob.herring@...xeda.com, pdeschrijver@...dia.com,
	pgaikwad@...dia.com, viresh.kumar@...aro.org, rnayak@...com,
	paul@...an.com, broonie@...nsource.wolfsonmicro.com,
	ccross@...roid.com, linux-arm-kernel@...ts.infradead.org,
	myungjoo.ham@...sung.com, rajagopal.venkat@...aro.org
Subject: Re: [PATCH v2 1/4] [RFC] clk: new locking scheme for reentrancy

On Wed, Aug 15, 2012 at 04:43:31PM -0700, Mike Turquette wrote:
> +void __clk_unprepare(struct clk *clk, struct clk *top)
> +{
>  	if (clk->ops->unprepare)
>  		clk->ops->unprepare(clk->hw);
>  
> -	__clk_unprepare(clk->parent);
> +	if (clk != top)
> +		__clk_unprepare(clk->parent, top);
> +}

The __clk_unprepare does not match the __clk_prepare below in terms of
if we should call clk->ops->prepare/unprepare on top clock.

I have to change __clk_unprepare to something like the below to get
the series work on imx6q.

 void __clk_unprepare(struct clk *clk, struct clk *top)
 {
+       if (clk == top)
+               return;
+
        if (clk->ops->unprepare)
                clk->ops->unprepare(clk->hw);

-       if (clk != top)
-               __clk_unprepare(clk->parent, top);
+       __clk_unprepare(clk->parent, top);
 }

> +int __clk_prepare(struct clk *clk, struct clk *top)
> +{
> +	int ret = 0;
> +
> +	if (clk != top) {
> +		ret = __clk_prepare(clk->parent, top);
>  		if (ret)
>  			return ret;
>  
>  		if (clk->ops->prepare) {
>  			ret = clk->ops->prepare(clk->hw);
>  			if (ret) {
> -				__clk_unprepare(clk->parent);
> +				/* this is safe since clk != top */
> +				__clk_unprepare(clk->parent, top);
>  				return ret;
>  			}
>  		}
>  	}
>  
> -	clk->prepare_count++;
> -
>  	return 0;
>  }

-- 
Regards,
Shawn
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