linux-kernel - Re: [patch] split MMC_CAP_4_BIT

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Date:	Fri, 11 Jan 2008 18:22:14 +0800
From:	"Bryan Wu" <cooloney.lkml@...il.com>
To:	"Pierre Ossman" <drzeus-mmc@...eus.cx>
Cc:	"Mike Frysinger" <vapier.adi@...il.com>,
	"Cai, Cliff" <Cliff.Cai@...log.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch] split MMC_CAP_4_BIT_DATA

On Jan 11, 2008 6:05 PM, Pierre Ossman <drzeus-mmc@...eus.cx> wrote:
> On Fri, 11 Jan 2008 04:47:44 -0500
> "Mike Frysinger" <vapier.adi@...il.com> wrote:
>
> > Cliff should be able to enumerate the cards he has tested and the
> > issues he's run into.  i'll see if i cant get more in depth
> > information from the hardware guys beyond the documentation on the sdh
> > already available in the hardware manual (which i'm guessing has not
> > been enough to appease you).
> >
>
> Great. And you're right in that the spec did not give any indication that MMC shouldn't work.
>

Our tester will reopen a tracker of this issue. When it's fired, you
will be updated with this information.

> I did notice one thing though. The pull-ups and pull-downs seem to be controllable. If I remember correctly, DAT3 needs to have a controller-side pull-up for MMC cards. And the docs said the default was not to provide that (in order to use the internal pull-up that most, but not all, SD cards have for detection). Might be something to look at if you haven't already.
>

I guess it is for MMC/SD card insert detection. Is it related with the
4-bit MMC and 4-bit SD?
Actually, there are some issues about the card insert detection on
BF54x SDH. Following is some comments of our bfin-sdh driver which is
in the development.

---
/* In term of ADSP_BF54x_Blackfin_Processor_Peripheral_Hardware_Reference,
 * the SDH allows software to detect a card when it is inserted into its slot.
 * The SD_DATA3 pin powers up low due to a special pull-down resistor. When an
 * SD Card is inserted in its slot, the resistance increases and a rising edge
 * is detected by the SDH module.
 * But this doesn't work sometimes. When a MMC/SD card is inserted, the voltage
 * doesn't rise on SD_DATA3. In term of The MultiMediaCard System Specification,
 * SD_DATA3 is used as CS pin in SPI mode. The MultiMediaCard wakes up in the
 * MultiMediaCard mode. During the scan procedure, host will send CMD0 to reset
 * MMC card, if CS pin is low, MMC card will enter SPI mode. Of course Secure
 * Digital Host controller is not a SPI controller. So the Card detect function
 * has to be disabled. After card is inserted run "echo 0 > /proc/driver/sdh"
 * to trigger card scanning */
---

Thanks
-Bryan Wu
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