[U-Boot] [PATCH] mmc: Do not poll using CMD13 when changing timing

[Marek Vasut]

On 6/25/19 4:13 PM, Jean-Jacques Hiblot wrote:
> Hi Marek,
> 
> On 06/02/2019 14:11, Marek Vasut wrote:
>> When using CMD6 to switch eMMC card timing from HS200/HS400 to HS/legacy,
>> do not poll for the completion status using CMD13, but rather wait 50mS.
>>
>> Once the card receives the CMD6 and starts executing it, the bus is in
>> undefined state until both the card finishes executing the command and
>> until the controller switches the bus to matching timing configuration.
>> During this time, it is not possible to transport any commands or data
>> across the bus, which includes the CMD13.
> 
> Is it something that affects all platforms ?
> 
> I've been working on this on TI platforms lately and although I've seen
> the same kind of problems. But they mostly go away If the code handling
> the switch handles the SWITCH_ERROR bit.

The error probably happens because you send the card a command, but the
command hits the bus that's in some weird intermediate state. Either the
card didn't finish switching the bus properties yet, or it did, or it's
in the middle of it, but you cannot tell.

[...]

-- 
Best regards,
Marek Vasut