linux-kernel - Re: [PATCH] clk: tegra: Don't enable PLLs during early boot

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Date:	Mon, 25 Mar 2013 10:12:43 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clk: tegra: Don't enable PLLs during early boot

On 03/25/2013 05:02 AM, Russell King - ARM Linux wrote:
> On Fri, Mar 22, 2013 at 09:48:11AM -0600, Stephen Warren wrote:
>> This assumption was made long ago. I know drivers are supposed to assume
>> that clocks are disabled when they're probed, but historically that
>> wasn't always the case, so if the audio drivers assumed that, and then
>> did clk_enable() as the first thing, they got a warning due to the
>> enabling an already enabled clock and/or later attempts to disable the
>> clocks wouldn't actually disable them.
> 
> No.  clocks have always been able to be enabled multiple times.  You
> should only get a warning if you try and disable it more times than you
> enabled it, because that's a violation of the API.

That may have been the issue; the clock may have been on at boot, and
hence the driver attempted to disable it without ever enabling it
itself, and this triggered an error/warning.

Equally, it's plausible this issue is long gone; the audio clocks were
set up this way due to issues over 2 years ago when the audio code was
upstreamed. At that time, Tegra's clock code was using very little
standard infra-structure, whereas now it's been cleaned up to use the
common clock framework etc.
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