Re: [RFC] How working MMC_BUS_WIDTH_TEST??

[Jaehoon Chung <jh80.chung@samsung.com>]

Hi Philip..

If i didn't set MMC_CAP_BUS_WIDTH_TEST,
entered mmc_compare_ext_csds(). right?

i understand that mmc_compare_ext_csds() compared with previously ext_csd.
But in source code, always previously ext_csd is NULL.

I didn't find where assigned ext_csd..

I think that need to assign ext_csd..

If my point is right, i will send the patch..

Thanks
Jaehoon Chung

Philip Rakity wrote:
> On Jun 28, 2011, at 9:42 PM, Jaehoon Chung wrote:
> 
>> Philip Rakity wrote:
>>> On Jun 28, 2011, at 3:54 AM, Jaehoon Chung wrote:
>>>
>>>> Hi..
>>>>
>>>> I found the MMC_CAP_BUS_WIDTH_TEST...
>>>> In mailing, I read the related patches..
>>>> but i didn't fully understand...
>>>>
>>>> /*
>>>> * If controller can't handle bus width test,
>>>> * compare ext_csd previously read in 1 bit mode
>>>> * against ext_csd at new bus width
>>>> */
>>>> if (!(host->caps & MMC_CAP_BUS_WIDTH_TEST))
>>>> 	err = mmc_compare_ext_csds(card,
>>>> 		ext_csd,
>>>> 		bus_width);
>>>> else
>>>> 	err = mmc_bus_test(card, bus_width);
>>>> if (!err)
>>>> 	break;
>>>>
>>>> And i tested suspend/resume..it's failed..
>>>> If i didn't set MMC_CAP_BUS_WIDTH_TEST, always return -EINVAL..
>>>> (using SDHCI controller, card is eMMC4.41)
>>>>
>>>> Didn't compare ext_csd's value..
>>>>
>>>> So i want to know how use MMC_CAP_BUS_WIDTH_TEST..
>>> I am using eMMC and code works fine so  maybe there is issue in no ext_csd.  You will need to
>>> add debug code to the compare_ext_csd and see what is not right and we can adjust the code.
>>> I am surprised that resume fails -- code will default to 1 bit data and it is NOT possible for this to
>>> be wrong.  At the moment -- clueless to explain with more information.
>>>
>>> TheCMD14/ CMD19 is in JEDEC spec for bus width testing.  Sends a pattern to the card and
>>> based on the returned values detects the bus width.  Some controllers do NOT support this command.
>>> The just do not work.  You need to figure this out by enabling the quirk.  No other way to know.
>> When card is probing, i think that need to test bus-width.
>> If card is non-removable, unnecessary bus_width test during resuming.
> 
> agree not necessary but does not explain error.
> 
> 
>> Because already know that support n-bit bus-width..how about this?
>>
>>> regards,
>>>
>>> Philip
>>>
>>>> Thanks,
>>>> Jaehoon Chung
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