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

[Jaehoon Chung]

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);
>> 	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

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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