Re: [PATCH 08/10] mmc: card: Use R1 response for the stop cmd at recovery path

[Adrian Hunter <adrian.hunter@intel.com>]

On 23/01/14 15:21, Ulf Hansson wrote:
> On 23 January 2014 11:09, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 22/01/14 17:00, Ulf Hansson wrote:
>>> Hosts supporting MMC_CAP_WAIT_WHILE_BUSY shall not be waiting for busy
>>> detection completion in the recovery path, which were the case when
>>> using R1B response.
>>>
>>> Start using R1 as response instead to align behavior, no matter if
>>> MMC_CAP_WAIT_WHILE_BUSY is supported or not.
>>
>> This does not make sense to me.  If you are sending a STOP command you
>> should use the correct response type.  R1B should be OK here because the
>> card should release the busy signal in any case except failure.
> 
> For those hosts not supporting MMC_CAP_WAIT_WHILE_BUSY a R1B is
> assumed to be treated same as an R1, which means there are no busy
> detection handled in the host.

That is not entirely true.  For hosts that do not set
MMC_CAP_WAIT_WHILE_BUSY we don't know if they wait or not.  I imagine most
do because it is more efficient, but the kernel has always been programmed
to poll the status anyway so you can't tell from the code.

MMC_CAP_WAIT_WHILE_BUSY was one of my inventions I am afraid.  If I recall
correctly it was mainly due to the SLEEP command because you can't poll in
that case and you don't want to delay the system from sleeping - if you are
certain that the controller has waited for busy to de-assert (i.e.
MMC_CAP_WAIT_WHILE_BUSY) then you can exit immediately.

> 
> mmc_blk_cmd_recovery() is the only caller of the send_stop() function.
> Additionally it does not care about to handle busy detection with
> CDM13 polling.
> 
> Now, since most hosts don't support MMC_CAP_WAIT_WHILE_BUSY which
> means there no busy detection done, I wanted to align to this
> behaviour - no matter if the host can do HW busy detection or not.
> 
> I am not saying this is how it must be done, just trying to provide
> you with some more reasons to why I wanted to change.
> 
> If we instead decide keep the R1B for send_stop(), we should implement
> CMD 13 polling to meet the same behaviour for hosts not supporting
> MMC_CAP_WAIT_WHILE_BUSY. In this scenario, we need to set a select a
> busy timeout, do you have any suggestion of what would be a reasonable
> value for it?

It is hard to tell if waiting is ever going to help more than hinder, so I
would not change this.

> 
> Kind regards
> Ulf Hansson
> 
>>
>>>
>>> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>>> ---
>>>  drivers/mmc/card/block.c |    2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>>> index 87cd2b0..74169fa 100644
>>> --- a/drivers/mmc/card/block.c
>>> +++ b/drivers/mmc/card/block.c
>>> @@ -728,7 +728,7 @@ static int send_stop(struct mmc_card *card, u32 *status)
>>>       int err;
>>>
>>>       cmd.opcode = MMC_STOP_TRANSMISSION;
>>> -     cmd.flags = MMC_RSP_SPI_R1B | MMC_RSP_R1B | MMC_CMD_AC;
>>> +     cmd.flags = MMC_RSP_SPI_R1 | MMC_RSP_R1 | MMC_CMD_AC;
>>>       err = mmc_wait_for_cmd(card->host, &cmd, 5);
>>>       if (err == 0)
>>>               *status = cmd.resp[0];
>>>
>>
> 
>