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

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Message-ID: <4B404E89.4060103@yahoo.es>
Date:	Sun, 03 Jan 2010 16:00:09 +0800
From:	Hein_Tibosch <hein_tibosch@...oo.es>
To:	Pierre Ossman <pierre@...man.eu>
CC:	Ben Nizette <bn@...sdigital.com>,
	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

Pierre Ossman wrote:
> 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.
>   
As I'm lucky to have main-stream cards that break the rule (on
avr32/AP7) I'll dive deeper into it and see if I can make it "automatic"
so that initialization will work for any of cards. Indeed using a kind
of 'bisect approach' approach.
... although I must say that before Sascha Hauer's patch, we never had
problems with any of the cards, using the controller's minimum freq of
137 Khz.

Hein



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