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

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Date:	Thu, 12 Jul 2012 12:50:46 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mike Turquette <mturquette@...com>, Pawel Moll <pawel.moll@....com>
Cc:	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 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.

Yours,
Linus Walleij
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