[U-Boot] [PATCH] powerpc/esdhc: force the bus width to 4bit

[Lukasz Majewski]

Hi Jaehoon,

> On 10/23/2012 06:50 PM, Marek Vasut wrote:
> > Dear Huang Changming-R66093,
> > 
> >> Best Regards
> >> Jerry Huang
> >>
> >>> -----Original Message-----
> >>> From: Marek Vasut [mailto:marex at denx.de]
> >>> Sent: Tuesday, October 23, 2012 3:24 PM
> >>> To: Huang Changming-R66093
> >>> Cc: u-boot at lists.denx.de; Andy Fleming
> >>> Subject: Re: [PATCH] powerpc/esdhc: force the bus width to 4bit
> >>>
> >>> Dear Chang-Ming.Huang at freescale.com,
> >>>
> >>>> From: Jerry Huang <Chang-Ming.Huang at freescale.com>
> >>>>
> >>>> For the current u-boot codes, only 4bit/1bit SD/SDHC bus width is
> >>>
> >>> support.
> >>>
> >>>> So for MMC card, we also support 4bit bus width, otherwiase, we
> >>>> will
> >>>
> >>>> get the 12bit bus width, which is not correct:
> >>> Andy ... can you please explain? I don't quite understand the
> >>> problem, I thought we had no problem supporting 8bit mmc (esp. if
> >>> the controller handles that for us mostly).
> >>
> >> Yes, the controller support 8bit MMC.
> >>
> >> FSL ESDHC driver set the host_caps = MMC_MODE_4BIT | MMC_MODE_8BIT;
> >> But, the current codes for MMC card has been changed to:
> >>
> >> } else {
> >> 	width = ((mmc->host_caps & MMC_MODE_MASK_WIDTH_BITS) >>
> >>                          MMC_MODE_WIDTH_BITS_SHIFT);

Hmm... looks like it is code done by me :-)
So little explanation shall be given.

This code is necessary for some targets (like Samsung's Goni) which can
only support 4 bit MMC mode.

> >> 	for (; width >= 0; width--) {
> >> 	....
> >>
> >> So for FSL ESDHC, the width = 3, after implement mmc_switch
> >> successfully, will set the bus to 4 * width. Therefore, I will get
> >> the 12bit (4 x 3) bus width.
> This problem is MMC subsystem's bug.
> I think good that will modify the code in mmc.c.
> If caps is set to MMC_MODE_4BIT | MMC_MODE_8BIT,
> we can see the 12bit support with using "mmcinfo" command
> 

The mmc_set_bus_width(mmc, 4 * width) in conjunction to above code
causes the problem.

I agree, that this code shall be refactored.
Lei, what do you think?


> Best Regards,
> Jaehoon Chung
> 
> >>
> >> Below is the old codes (width = 2):
> >> } else {
> >>                 for (width = EXT_CSD_BUS_WIDTH_8; width >= 0;
> >> width--) {
> > [...]
> > 
> > 
> > Uh, so it's a bug in the MMC subsystem?
> > Best regards,
> > Marek Vasut
> > _______________________________________________
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> > U-Boot at lists.denx.de
> > http://lists.denx.de/mailman/listinfo/u-boot
> > 
> 
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-- 
Best regards,

Lukasz Majewski

Samsung Poland R&D Center | Linux Platform Group