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

[Huang Changming-R66093]

Best Regards
Jerry Huang


> -----Original Message-----
> From: u-boot-bounces at lists.denx.de [mailto:u-boot-bounces at lists.denx.de]
> On Behalf Of Andy Fleming
> Sent: Thursday, November 01, 2012 12:09 PM
> To: Lukasz Majewski
> Cc: Jaehoon Chung; Marek Vasut; Lei Wen; u-boot at lists.denx.de
> Subject: Re: [U-Boot] [PATCH] powerpc/esdhc: force the bus width to 4bit
> 
> >
> > 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?
> 
> 
> I am... very confused by this whole thread. And the code associated with
> it. The host_caps field has a bitmask which declares the widths supported
> by a given controller.
> 
> What would possess you to index them by addition, and convert their
> values by multiplication?? It's a bitfield! I'm embarrassed that I
> allowed this code in, and will review future submissions from you with a
> very skeptical eye.
> 
> Ah, and further review indicates it is Lei Wen who introduced the idea of
> iterating through a bitfield by subtraction, though I can see how
> iterating through the EXT_CSD *field* definition (which looks a lot like
> a bitfield, but may not be) *might* be considered reasonable.
> 
> Meanwhile, Huang Changming, why would you see this broken code, and then
> decide the best workaround was to cripple our controller by eliminating
> support for 8-bit?
I see 12bit width when using mmcinfo, then found out the mmc.c has been changed, and I assume this change is right,
So I have to force our controller to just support 4bit width, otherwise, the 12bit bus width is not correct.