linux-kernel - Re: [PATCH v3] mmc: Make ID freq configurable

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Date:	Sun, 3 Jan 2010 00:38:04 +0100
From:	Pierre Ossman <pierre@...man.eu>
To:	Ben Nizette <bn@...sdigital.com>
Cc:	Hein_Tibosch <hein_tibosch@...oo.es>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Adrian Hunter <adrian.hunter@...ia.com>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Matt Fleming <matt@...sole-pimps.org>
Subject: Re: [PATCH v3] mmc: Make ID freq configurable

On Sun, 3 Jan 2010 09:23:30 +1100
Ben Nizette <bn@...sdigital.com> wrote:

> > 
> > Broken cards seem to be all over the spectrum, so I wouldn't be
> > suprised if you find ones that break if you go too low as well.
> 
> Yea good point, though given there might not even be a One Freq to Rule Them All, how about:
> 
> ---8<---
> 
> From: Ben Nizette <bn@...sdigital.com>
> Subject: [PATCH v3] mmc: Make ID freq configurable
> 
> While the SD spec specifies a range of frequencies for the ID phase from 100-400kHz, not all cards play by the rules.  This patch adds a Kconfig option to allow the user to tweak this to their card/host config, though the default of 250kHz should be fine for all spec-abiding cards and most others besides.
> 
> Signed-off-by: Ben Nizette <bn@...sdigital.com>
> 

This is not a good solution. We all use the same pool of cards so we
should all be using the same init sequence. If there isn't a single
frequency where all cards will work, then we'll have to make something
more advanced where the kernel will try the init several times with
different clocking.

Rgds
-- 
     -- Pierre Ossman

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