linux-kernel - Re: [PATCH] clk: allow clocks without parents to change rate

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Message-ID: <20120712165418.GJ2772@gmail.com>
Date:	Thu, 12 Jul 2012 09:54:18 -0700
From:	Mike Turquette <mturquette@...com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Pawel Moll <pawel.moll@....com>,
	Mike Turquette <mturquette@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...nel.org, Ulf Hansson <ulf.hansson@...ricsson.com>
Subject: Re: [PATCH] clk: allow clocks without parents to change rate

On 20120712-12:50, Linus Walleij wrote:
> On Thu, Jul 12, 2012 at 1:42 AM, Mike Turquette <mturquette@...com> wrote:
> 
> > This has been fixed in Pawell's patch, "clk: Check parent for NULL in
> > clk_change_rate".
> 
> Yes, that'll probably work.
> 
> A small nitpick though:
> 
> I have slightly different semantics, Pawel's patch assigns zero if
> parent is NULL, then use that as fallback, whereas I check for the
> parent being NULL all the way. I was worried that the old sematics
> could change like this:
> 
> So here it takes that:
> 
> +       if (clk->parent)
> +               best_parent_rate = clk->parent->rate;
> +
> 
> And I was cautious that if this changes the parent rate:
> 
> +               clk->ops->set_rate(clk->hw, clk->new_rate, best_parent_rate);
> 
> Then this passes the old parent rate to the recalc function:
> 
> +               clk->rate = clk->ops->recalc_rate(clk->hw, best_parent_rate);
> 
> It has no side-effects on my system but I worried about
> others, so I just left the behaviour to re-read the rate from the parent
> every time if possible.
> 

Thanks for looking into it.  I think for now let's keep what we have and
we'll patch it up if bugs are reported.

Thanks again,
Mike

> Yours,
> Linus Walleij
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