linux-kernel - Re: [PATCH v2] mmc: lower init clock frequency to 300kHz

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Date:	Sat, 2 Jan 2010 20:07:01 +1100
From:	Ben Nizette <bn@...sdigital.com>
To:	Hein_Tibosch <hein_tibosch@...oo.es>
Cc:	Pierre Ossman <pierre@...man.eu>,
	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 v2] mmc: lower init clock frequency to 300kHz


(Adding linux CCs)

On 02/01/2010, at 7:19 PM, Hein_Tibosch wrote:

> Almost good: on my Kingston Elite Pro (50x) SD-card, initialization will
> only succeed if F <= 282258 Hz.

...

> 
> I checked some datasheets of several makes:
> 
> Delkin microSD min 0 max 400
> Swissbit min 0 max 400
> Sandisk 100 - 400
> Toshiba 100 - 400
> ST electronics 0 400
> SD-specification: Issue continues clock in frequency range of 100KHz-400KHz
>  If the Average frequency of the SDCLK is less than 100KHz then the card
>  may not be able to respond within the 1-second limit
> 
> So what about 100 or 150 Khz?

Ah geez, yeah this something else I was hoping to avoid with the V1 patch - an endless stream of "oh shit, this card's even /moore/ broken!  Patch it, patch it good"

Pierre, thoughts?  All my cards were borderline spec but Hein's got a mainstream, common card which seems to completely ignore the spec.  Can we just take the few-hundred-uS hit and allow initialization down at the bottom end, say 100kHz?

<overkill> Or a KConfig option? </overkill>

	--Ben.

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