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Message-ID: <4A7A08FE.5000909@mnementh.co.uk>
Date: Wed, 05 Aug 2009 23:34:38 +0100
From: Ian Molton <ian@...menth.co.uk>
To: Guennadi Liakhovetski <g.liakhovetski@....de>
CC: Magnus Damm <magnus.damm@...il.com>,
pHilipp Zabel <philipp.zabel@...il.com>,
Paul Mundt <lethal@...ux-sh.org>,
Mark Brown <broonie@...nsource.wolfsonmicro.com>,
linux-kernel@...r.kernel.org, Pierre Ossman <drzeus@...eus.cx>,
Magnus Damm <damm@...nsource.se>
Subject: Re: MMC: Make the configuration memory resource optional
Guennadi Liakhovetski wrote:
> How do we verify this? Do I need some "very fast" card, so that sd would
> try to drive the clock beyond pdata->hclk / 2, which should then fail?
One way would be a 'scope on the card pins, but since you havent said I
am assuming you have not altered the clock-speed setting routine.
Here you can see why I didnt like the silently-drop-conf-accesses
version of the patch. If you had not made conf area accesses silently
succeed, you'd have found one lurking in the set_clock function.
Since your controller has no CNF area, it was discarding the write to
the 1:1 clock bit (that isnt in its none-existant conf area) and thus
you got the next lowest clock as a result (/2)
> Currently I'm using 24MHz (copied from the original driver), and the only
> thing I know about the controller is its "Maximum operating frequency: 25
> MHz."
Thats the HCLK frequency, not the card clock.
the TMIO MFD devices can divide this HCLK by anything from 512 to 2, and
MFD devices have a facility to disable the divider, yielding full HCLK
speed as the card clock.
If you havent already found a 1:1 clock enable bit on your device, you
might try looking for it - it'd yield a near linear factor-of-two speed
increase.
-Ian
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