linux-kernel - Re: [PATCH E 11/14] OMAP clock: track child clocks

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Date:	Mon, 2 Mar 2009 16:02:14 -0700 (MST)
From:	Paul Walmsley <paul@...an.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	"Woodruff, Richard" <r-woodruff2@...com>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH E 11/14] OMAP clock: track child clocks

Hello Russell,

On Mon, 23 Feb 2009, Russell King - ARM Linux wrote:

> On Thu, Feb 19, 2009 at 06:50:52PM -0600, Woodruff, Richard wrote:
> > The historic usage of this has been against single use leaf clocks (1st instance of gptimer).  When it was used it did:
> >         clk_get()
> >         clk_set_parent()
> >         clk_enable()
> > 
> > This usage was ok for that. Use on a disabled clock is needed.
> > 
> > If there are multiple users on the clock or it is enabled there are problems.
> 
> It sounds to me like clk_set_parent() needs this then to prevent enabled
> clocks being reparented.  By doing so, we no longer need to disable/enable
> the clock within the OMAP2/3 set_parent function since we are now
> guaranteed that the clock will be disabled.
> 
> Ack?

One suggestion on the patch:

> diff --git a/arch/arm/plat-omap/clock.c b/arch/arm/plat-omap/clock.c
> index 08baa18..b2d9e1f 100644
> --- a/arch/arm/plat-omap/clock.c
> +++ b/arch/arm/plat-omap/clock.c
> @@ -144,12 +144,14 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
>  		return ret;
>  
>  	spin_lock_irqsave(&clockfw_lock, flags);
> -	if (arch_clock->clk_set_parent)
> -		ret = arch_clock->clk_set_parent(clk, parent);
> -	if (ret == 0) {
> -		if (clk->recalc)
> -			clk->rate = clk->recalc(clk);
> -		propagate_rate(clk);
> +	if (clk->usecount == 0) {
> +		if (arch_clock->clk_set_parent)
> +			ret = arch_clock->clk_set_parent(clk, parent);
> +		if (ret == 0) {
> +			if (clk->recalc)
> +				clk->rate = clk->recalc(clk);
> +			propagate_rate(clk);
> +		}
>  	}
>  	spin_unlock_irqrestore(&clockfw_lock, flags);

Suggest returning a more specific error than -EINVAL:

if (clk->usecount > 0)
        return -EBUSY;




- Paul
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