linux-kernel - Re: MMCv4 support (8-bit support missing)

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Date:	Wed, 18 Apr 2007 16:21:07 +0200
From:	Pierre Ossman <drzeus@...eus.cx>
To:	Madhusudhan c <cr.madhusudhan@...il.com>
CC:	linux-kernel@...r.kernel.org, philipl@...rt.org
Subject: Re: MMCv4 support (8-bit support missing)

Madhusudhan c wrote:
> 
> Kyung-ju Hyun from samsung had submitted a patch for MMCPlus support
> long back, which had the bus testing procedure implemented and it
> works fine. I am able to write and read the data pattern back
> successfuly with his patch. I am not sure why his patch was not
> integrated into the main line kernel.
> 

I don't think I've seen that patch. And now we have the work by Philip and
myself which adds support for both MMC 4.0 and 4.2. The only missing piece is
8-bit data and I'm not that interested in adding it until we have a driver that
can use it.

> Why should we be bothered about how controllers respond at the MMC
> core level. We need to just implement what specification says and
> leave the controller handling part to the controller driver. Am I
> correct?

Kindof. The controller drivers should indeed just handle the controller and
leave the protocol stuff to the mmc core. The problem is that this bus testing
stuff breaks the previous standards. Sending invalid CRC was not previously a
supported operation, so many controllers just toss the data when that happens.
And since the bus testing is specified as a test, not a required part of the
wide bus song and dance, we've decided to leave it out.

Rgds
Pierre

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