linux-kernel - Re: [patch] split MMC_CAP_4_BIT

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Message-ID: <20080111094036.4c683791@poseidon.drzeus.cx>
Date:	Fri, 11 Jan 2008 09:40:36 +0100
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	"Bryan Wu" <cooloney.lkml@...il.com>
Cc:	"Cai, Cliff" <Cliff.Cai@...log.com>,
	"Mike Frysinger" <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] split MMC_CAP_4_BIT_DATA

On Fri, 11 Jan 2008 14:17:01 +0800
"Bryan Wu" <cooloney.lkml@...il.com> wrote:

> We were told this is an hardware design issue, so please help us to
> workaround it in software side with Mike's patch.

I'm afraid that's insufficient motivation for this change. All documentation and real world tests say that MMC and SD 4-bit data is 100% compatible. So it's far more probable that you've misdiagnosed your error than this being the actual problem. The fact that 4-bit MMC support has been present for some time and you're only now seeing a problem further supports that.

In light of that, the suggested patch would not only be incorrect, it would also be worse than doing nothing. You would be papering over a symptom, making the real problem harder to find.

If you want something ready for upstream, for now I suggest removing MMC_CAP_4_BIT_DATA completely from your driver's caps field.

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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