Re: [RFC] How working MMC_BUS_WIDTH_TEST??

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

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.
Because already know that support n-bit bus-width..how about this?

> 
> regards,
> 
> Philip
> 
>> Thanks,
>> Jaehoon Chung
> 
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