linux-kernel - Re: [PATCH] pwm: mxs: fix period divider computation

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Date:	Wed, 11 Mar 2015 11:57:30 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	Gaetan Hug <ghug@...uct.be>, linux-pwm@...r.kernel.org,
	linux-kernel@...r.kernel.org, fabio.estevam@...escale.com
Subject: Re: [PATCH] pwm: mxs: fix period divider computation

On Mon, Mar 02, 2015 at 08:32:09PM +0800, Shawn Guo wrote:
> On Wed, Feb 18, 2015 at 02:06:34PM +0100, Gaetan Hug wrote:
> > The driver computes which clock divider it sould be using from the
> > requested period. This computation assumes that the link between the
> > register value and the actual divider value is raising 2 to the power of
> > the registry value.
> > 
> >     div = 1 << regvalue
> > 
> > This is true only for the first 5 values out of 8. Next values are 64,
> > 256 and, 1024 - instead of 32, 64, 128.
> 
> Just checked i.MX28 Reference Manual, and yes, this is the case.
> 
> > This affects only the users requesting a period > 0.04369s.
> > 
> > Replace the computation with a look-up table.
> 
> Your SoB is missing here.  Otherwise,
> 
> Acked-by: Shawn Guo <shawn.guo@...aro.org>

Gaetan,

can you resend with your Signed-off-by added? Or at least provide it
here? I can't really apply this without one.

Thierry

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