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

[Andy Fleming]

>
> 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'm going to fix this right now. Probably in the quite sensible way
that Jaehoon Chung suggested.

Andy