Re: [PATCH 4/4] mmc: core: Don't use ->card_busy() and CMD13 in combination when polling

[Ulf Hansson <ulf.hansson@linaro.org>]

On 21 October 2016 at 11:19, Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 20/10/16 11:19, Ulf Hansson wrote:
>> When polling for busy after sending a MMC_SWITCH command, both the optional
>> ->card_busy() callback and CMD13 are being used in conjunction.
>>
>> This doesn't make sense. Instead it's more reasonable to rely solely on the
>> ->card_busy() callback when it exists. Let's change that and instead use
>> the CMD13 as a fall-back. In this way we avoid sending CMD13, unless it's
>> really needed.
>>
>> Within this context, let's also take the opportunity to make some
>> additional clean-ups and clarifications to the related code.
>>
>> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>> ---
>>  drivers/mmc/core/mmc_ops.c | 30 ++++++++++++++----------------
>>  1 file changed, 14 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
>> index a84a880..481bbdb 100644
>> --- a/drivers/mmc/core/mmc_ops.c
>> +++ b/drivers/mmc/core/mmc_ops.c
>> @@ -495,34 +495,32 @@ static int mmc_poll_for_busy(struct mmc_card *card, unsigned int timeout_ms,
>>       timeout = jiffies + msecs_to_jiffies(timeout_ms) + 1;
>>       do {
>>               /*
>> -              * Due to the possibility of being preempted after
>> -              * sending the status command, check the expiration
>> -              * time first.
>> +              * Due to the possibility of being preempted while polling,
>> +              * check the expiration time first.
>>                */
>>               expired = time_after(jiffies, timeout);
>> -             if (send_status) {
>> +
>> +             if (host->ops->card_busy) {
>> +                     busy = host->ops->card_busy(host);
>
> I didn't really have time to look at these patches, sorry :-(.  But this
> loop looks like it could use a cond_resched()

Yes, something like that is definitely needed! Although, I suggest we
do that improvement on top of this change, if you are fine with that
approach?

The reason is that I am also pondering over, whether it could make
sense to poll with a dynamically increased interval. At least when
using ->card_busy().
Let's say by starting at 1 us interval, then at each poll attempt we
double the interval time. We would then rather use a combination of
udelay(), usleep_range() and msleep() to accomplish what you propose.
Does that make sense to you?

Kind regards
Uffe