linux-kernel - Re: [PATCH 7/7] mmc_spi: support for non-byte-aligned cards

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Message-ID: <87a5b0800903110738h508aae87y7fc462d30cc89c7f@mail.gmail.com>
Date:	Wed, 11 Mar 2009 14:38:09 +0000
From:	Will Newton <will.newton@...il.com>
To:	Wolfgang Mües <wolfgang.mues@...rswald.de>
Cc:	Pierre Ossman <drzeus@...eus.cx>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Fleming <matt@...sole-pimps.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Mike Frysinger <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] mmc_spi: support for non-byte-aligned cards

On Wed, Mar 11, 2009 at 2:34 PM, Wolfgang Mües
<wolfgang.mues@...rswald.de> wrote:
> Will,
>
> Am Mittwoch, 11. März 2009 schrieb Will Newton:
>> <wolfgang.mues@...rswald.de> wrote:
>> > From: Wolfgang Muees <wolfgang.mues@...rswald.de>
>> >
>> > o A very large subset of SD cards in the market send their
>> >  responses and data non-byte-aligned. So add logic to the
>> >  mmc spi driver to handle this mess.
>>
>> Are you sure about this?
>
> Yes.
>
>> Do you have any further references for this
>> or examples of cards that exhibit this problem?
>
> Kingston. The 1 GByte SD card, and a 128 MByte microSD card. I have got some
> reports from other mmc spi users with the same problem.

Are they using the same host controller? Have you tried these cards
with a different host controller?

Are you clocking them particularly slow or fast?

> The SD protocoll ist NOT byte-aligned. Messages are starting with a
> leading "0" bit. I think some chip vendors have adapted the SPI mode from SD
> mode and forgotten to do propper byte alignment.
>
>> Are you sure your SPI host controller is operating correctly?
>
> Yes. My logic probe gives the same results as my spi host controller.
> For some cards, you can see the bit offset is getting larger if the
> controller on the SD card is getting more and more busy...

A logic probe may not display any signal integrity issues you might have.
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