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

[Jaehoon Chung]

Hi, Lukasz,
>>>>>> 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.
then how about using the width[idx] like kernel?

Best Regards,
Jaehoon Chung
> 
> 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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>>
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> 
> 
>