linux-kernel - Re: [patch] split MMC_CAP_4_BIT

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Date:	Fri, 11 Jan 2008 01:25:01 -0500
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Bryan Wu" <cooloney.lkml@...il.com>
Cc:	"Pierre Ossman" <drzeus-mmc@...eus.cx>,
	"Cai, Cliff" <Cliff.Cai@...log.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch] split MMC_CAP_4_BIT_DATA

On Jan 11, 2008 1:17 AM, Bryan Wu <cooloney.lkml@...il.com> wrote:
> On Jan 10, 2008 7:57 PM, Pierre Ossman <drzeus-mmc@...eus.cx> wrote:
> > On Thu, 10 Jan 2008 17:22:55 +0800
> > "Bryan Wu" <cooloney.lkml@...il.com> wrote:
> >
> > >
> > > At page 4-3 of  ADSP-BF54x Blackfin(R) Processor Peripheral Hardware
> > > Reference, there is a table which guide us the SDH controller does not
> > > support 4-bit mode MMC card. Please found the table picture in the
> > > attachment or get the document at:
> > > http://www.analog.com/UploadedFiles/Associated_Docs/61460151169789ADSP_BF54x_Blackfin_Processor_Peripheral_Hardware_Reference.pdf
> > >
> >
> > Ok, but this just means the controller wasn't designed with 4-bit MMC in mind. As several other "SD-only" controller have been tested with modern MMC cards without a problem, this is not sufficient to explain any problem.
> >
>
> This should be some HW design issue and BF54x including SDH controller
> is in mass production.
> There is no chance to change the silicon, we just wanna use software
> driver to workaround this issue.
> So Mike's patch is here.
>
> > >
> > > Thanks, actually we are not yet convinced  by our hardware designer
> > > why BF54x SDH does not support 4-bit MMC.
> > >
> >
> > Please keep me informed on how it progresses. I'd like an at least plausible explanation, preferably also some empirical data, before I'm ready to accept Mike's patch.
> >
>
> We were told this is an hardware design issue, so please help us to
> workaround it in software side with Mike's patch.
> And how do you think my suggestion to Mike's patch,
> #define MMC_CAP_4_BIT_DATA ( MMC_CAP_SD_4_BIT_DATA | MMC_CAP_MMC_4_BIT_DATA)
> Then no need to change other MMC host drivers

i can send an updated patch as needed.  i think Bryan's suggestion
here is a good one.
-mike
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