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

[Jean-Jacques Hiblot]

On 25/06/2019 17:53, Marek Vasut wrote:
> 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.

OK thanks for the response.

If CMD13 can't be used because the bus is in an undefined state, 
shouldn't send_cmd(CMD13) just fail ?

I'm asking because this is a 50ms delay in the hot path of the boot 
process.

JJ


>
> [...]
>