linux-kernel - Re: [PATCH 2/7] ARM: tegra: clock: Round rate before setting rate

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Message-ID: <AANLkTikV4++xA6JCh2yx_krdJrFddioZjBWe9pHP0b-x@mail.gmail.com>
Date:	Mon, 21 Feb 2011 21:26:04 -0800
From:	Olof Johansson <olof@...om.net>
To:	Colin Cross <ccross@...roid.com>
Cc:	linux-tegra@...r.kernel.org, konkers@...roid.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mike@...pulab.co.il, Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 2/7] ARM: tegra: clock: Round rate before setting rate

On Mon, Feb 21, 2011 at 6:39 PM, Colin Cross <ccross@...roid.com> wrote:
> Call the clock's round_rate op, if it exists, before calling
> the set_rate op.  This will help later when dvfs is added,
> dvfs needs to know what the final rate will be before the
> frequency changes.
>
> Also requires fixes to the round rate functions to ensure
> calling round rate and then set rate will not cause the
> frequency to be rounded down twice.  When picking clock
> divider values, the clock framework picks the closest
> frequency that is lower than the requested frequency.  If
> the new frequency calculated from the divider value is
> rounded down, and then passed to set_rate, it will get
> rounded down again, possibly resulting in a frequency two
> steps lower than the original requested frequency.
>
> Fix the problem by rounding up when calculating the frequency
> coming out of a clock divider, so if that frequency is
> requested again, the same divider value will be picked.
>
> Signed-off-by: Colin Cross <ccross@...roid.com>

Acked-by: Olof Johansson <olof@...om.net>
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