linux-kernel - RE: [PATCH] [ARM] twd: Allow twd rescaling to match cpu frequency

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Date:	Fri, 12 Nov 2010 13:49:50 +0100
From:	Harald Gustafsson <harald.gustafsson@...csson.com>
To:	Linus Walleij <linus.ml.walleij@...il.com>,
	Colin Cross <ccross@...roid.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	srinidhi kasagar <srinidhi.kasagar@...ricsson.com>,
	Varun Swara <Varun.Swara@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Rickard ANDERSSON <Rickard.Andersson@...ricsson.com>
Subject: RE: [PATCH] [ARM] twd: Allow twd rescaling to match cpu frequency

Hi,

Don't forget the other patches to make this work:

[ARM] twd: Always calibrate local timer
[ARM] twd: Fix updating control register in set_mode
[ARM] twd: Fix prescaler getting cleared by set_mode

/Harald Gustafsson
________________________________________
From: Linus Walleij [linus.ml.walleij@...il.com]
Sent: Friday, November 12, 2010 1:39 PM
To: Colin Cross
Cc: linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; Russell King; srinidhi kasagar; Varun Swara; Catalin Marinas; Harald Gustafsson; Rickard ANDERSSON
Subject: Re: [PATCH] [ARM] twd: Allow twd rescaling to match cpu frequency

Hi Colin,

2010/9/2 Colin Cross <ccross@...roid.com>:

> The clock to the ARM TWD local timer scales with the cpu
> frequency.  To allow the cpu frequency to change while
> maintaining a constant TWD frequency, pick a lower target
> frequency for the TWD and use the prescaler to divide down
> to the closest lower frequency.
>
> This patch provides a new initialization function that takes
> a target TWD frequency and the relation between the cpu
> clock and the TWD clock, required to be an integer divider
>>= 2 by the ARM spec.  It also provides a function to be
> called from cpufreq drivers to set the prescaler whenever
> the cpu frequency changes.

What's the status of this patch?

We have basically the same problem so we'd really like
a generic solution to this problem.

Our only comment is that we cannot see the reason for
not using the CPUfreq notifiers as most scaling code
is, but I assume there is some specific reason for this?

Unless something holds this back, could you post it to
Russells patch tracker, we might have an add-on patch
for the U8500 later.

Yours,
Linus Walleij
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