linux-kernel - Re: [patch] split MMC_CAP_4_BIT

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Date:	Thu, 10 Jan 2008 17:22:55 +0800
From:	"Bryan Wu" <cooloney.lkml@...il.com>
To:	"Pierre Ossman" <drzeus-mmc@...eus.cx>
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 Jan 10, 2008 4:54 PM, Pierre Ossman <drzeus-mmc@...eus.cx> wrote:
> On Thu, 10 Jan 2008 00:45:27 +0800
> "Bryan Wu" <cooloney.lkml@...il.com> wrote:
>
> >
> > Actually, Blackfin BF54x on-chip SDIO host controller is supposed to
> > support 1-bit and 4-bit MMC or SD. But in the real platform, when MMC
> > works at 4-bit mode there will be a FIFO underrun error
> > (http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=3535).
> > While SD works at 4-bit mode is OK. We believe this is a hardware
> > issue of the SDIO host controller of BF54x.
>
> Odd. As there shouldn't be a difference, I'm inclined to believe that this is card dependent. So it could as well appear with some SD cards as well.
>

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

> How much have you tested this issue? That tracker entry isn't very verbose.
>
> Also, how can an underrun appear? The system should have flow control. And an underrun does not sound like a bus problem, rather that you have a card with different speed characteristics than the hardware/driver can handle.
>

I am sorry for this mistake. This tracker is not for this 4-bit issue,
it is another bug which should be fixed by Cliff.

> >
> > We intend to workaround in our own BF54x SDIO host controller driver,
> > but there is no place for us to determine MMC or SD. One choice is to
> > hack common code like this:
>
> _If_ it truly cannot handle 4-bit MMC, then Mike's patch is the way to go. But I'm not yet convinced that the problem is related to MMC vs SD.
>

Thanks, actually we are not yet convinced  by our hardware designer
why BF54x SDH does not support 4-bit MMC.

>
> 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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