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

[Jaehoon Chung]

Hi Lukasz,

	width = ((mmc->host_caps & MMC_MODE_MASK_WIDTH_BITS) >>
	                          MMC_MODE_WIDTH_BITS_SHIFT);

This code has the problem. If width is set to 0x3,
then BUS_WIDTH field of ext_csd register is set to 0x3.
Value 0x3 is nothing.(It's reserved)
If we want to set 4-bit, then that value is set to 0x2.
This problem need to fix.
I will send the patch for this problem.

Best Regards,
Jaehoon Chung

On 10/31/2012 05:20 PM, Lukasz Majewski wrote:
> Hi Jaehoon,
> 
>> 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?
> 
> I don't mind :-) if it works at 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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>>
> 
> 
>