linux-kernel - Re: [PATCH 9/9] clk: tegra210: Initialize PLL

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Message-ID: <56967ADD.8090904@nvidia.com>
Date:	Wed, 13 Jan 2016 11:27:09 -0500
From:	Rhyland Klein <rklein@...dia.com>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Peter De Schrijver <pdeschrijver@...dia.com>,
	Mike Turquette <mturquette@...libre.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Bill Huang <bilhuang@...dia.com>, Jim Lin <jilin@...dia.com>,
	Benson Leung <bleung@...omium.org>,
	<linux-clk@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 9/9] clk: tegra210: Initialize PLL_D2 to a sane rate

On 1/13/2016 9:03 AM, Thierry Reding wrote:
> * PGP Signed by an unknown key
> 
> On Fri, Jan 08, 2016 at 01:45:14PM -0500, Rhyland Klein wrote:
>> Initialize PLL_D2 to a sane rate at the start of the day.
>>
>> Signed-off-by: Rhyland Klein <rklein@...dia.com>
>> ---
>>  drivers/clk/tegra/clk-tegra210.c | 1 +
>>  1 file changed, 1 insertion(+)
> 
> There are a lot of assumptions in this commit message. I'm asking myself
> why does it need to be initialized to any rate at all? Isn't it up to
> the user driver to set the PLL to whatever it knows to be a sane rate?
> Why is 594 MHz a sane rate?
> 
> A good commit message should answer those questions.
> 

Thanks. This patch came about in response to some work with
suspend/resume logic in the ChromeOS kernel. In the suspend/resume patch
there, it reads all clk rates and caches them in suspend, then re-sets
them on resume. We hadn't been using pll_d2 at all, and its rate (when
read in suspend()) came back as 0. Then in resume, we would tr to set
it, clk_set_rate(pll_d2, 0) and would generate a warning/error that 0
wasn't a valid rate.

As for the specific rate I chose, I simply took one off the table of
supported frequencies in the clk-tegra210 code, so that it was non-zero.

Since we don't support suspend/resume right now in the clk drivers, I
don't think its urgent to merge this patch. I can drop in in the next
rev if thats easier.

-rhyland

-- 
nvpublic