Re: [PATCH V6 08/15] mmc: mmc: Hold re-tuning if the card is put to sleep

Adrian Hunter
2015-05-06T10:30:46Z

On 06/05/15 12:32, Ulf Hansson wrote:
> On 6 May 2015 at 10:39, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> On 04/05/15 16:44, Ulf Hansson wrote:
>>> On 20 April 2015 at 14:09, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>> Currently "mmc sleep" is used before power off and
>>>> is not paired with waking up. Nevertheless hold
>>>> re-tuning.
>>>>
>>>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>>>> ---
>>>> drivers/mmc/core/mmc.c | 14 +++++++++++---
>>>> 1 file changed, 11 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>>> index f36c76f..daf9954 100644
>>>> --- a/drivers/mmc/core/mmc.c
>>>> +++ b/drivers/mmc/core/mmc.c
>>>> @@ -21,6 +21,7 @@
>>>> #include <linux/mmc/mmc.h>
>>>>
>>>> #include "core.h"
>>>> +#include "host.h"
>>>> #include "bus.h"
>>>> #include "mmc_ops.h"
>>>> #include "sd_ops.h"
>>>> @@ -1504,6 +1505,7 @@ static int mmc_can_sleep(struct mmc_card *card)
>>>> return (card && card->ext_csd.rev >= 3);
>>>> }
>>>>
>>>> +/* If necessary, callers must hold re-tuning */
>>>
>>> Remove this comment.
>>>
>>>> static int mmc_sleep(struct mmc_host *host)
>>>> {
>>>> struct mmc_command cmd = {0};
>>>> @@ -1631,6 +1633,7 @@ static int _mmc_suspend(struct mmc_host *host, bool is_suspend)
>>>> int err = 0;
>>>> unsigned int notify_type = is_suspend ? EXT_CSD_POWER_OFF_SHORT :
>>>> EXT_CSD_POWER_OFF_LONG;
>>>> + bool retune_release = false;
>>>>
>>>> BUG_ON(!host);
>>>> BUG_ON(!host->card);
>>>> @@ -1651,17 +1654,22 @@ static int _mmc_suspend(struct mmc_host *host, bool is_suspend)
>>>> goto out;
>>>>
>>>> if (mmc_can_poweroff_notify(host->card) &&
>>>> - ((host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) || !is_suspend))
>>>> + ((host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) || !is_suspend)) {
>>>> err = mmc_poweroff_notify(host->card, notify_type);
>>>> - else if (mmc_can_sleep(host->card))
>>>> + } else if (mmc_can_sleep(host->card)) {
>>>> + mmc_retune_hold(host);
>>>> err = mmc_sleep(host);
>>>> - else if (!mmc_host_is_spi(host))
>>>> + } else if (!mmc_host_is_spi(host)) {
>>>> err = mmc_deselect_cards(host);
>>>> + }
>>>>
>>>> if (!err) {
>>>> mmc_power_off(host);
>>>> mmc_card_set_suspended(host->card);
>>>> }
>>>> +
>>>> + if (retune_release)
>>>> + mmc_retune_release(host);
>>>> out:
>>>> mmc_release_host(host);
>>>> return err;
>>>
>>> Instead of add mmc_retune_hold|release() to _mmc_suspend(), I would
>>> like you to move that handling into mmc_sleep(). The code should be
>>> easier and it becomes more clear that it's because of a command
>>> sequence.
>>>
>>> I think mmc_retune_hold() should be invoked before mmc_wait_for_cmd()
>>> and then mmc_retune_release() just after, in mmc_sleep(). That should
>>> work, right!?
>>
>> That would be the same as holding re-tuning for that request, which is
>> what already happens i.e. adding hold()/release() around mmc_wait_for_cmd()
>> is redundant.
>
> I don't understand your point, sorry.

mmc_wait_for_cmd() calls mmc_wait_for_req() which calls __mmc_start_req()
which calls mmc_start_request() which calls mmc_retune_hold()

Then mmc_wait_for_req() calls mmc_wait_for_req_done() which calls
mmc_retune_release().

So
mmc_wait_for_cmd() (with no retries)
has the same effect as
mmc_retune_hold()
mmc_wait_for_cmd()
mmc_retune_release()

>
> Anyway, my proposal didn't quite work, which is due to that
> mmc_deselect_cards() (invoked from mmc_sleep()) deals with retries. If
> there had been only one try, I thought it could be okay to have that
> command to be preceded by a re-tune.
>
> Anyway, I would like you to move the mmc_retune_hold|release() calls
> into the mmc_sleep() function.

That would have no effect as explained above.

>
>>
>> The options for the caller are:
>>
>> 1)
>> hold re-tuning
>> put emmc to sleep
>> later wake up emmc
>> release re-tuning
>>
>> 2)
>> put emmc to sleep
>> later increment hold_count
>> wake up emmc ignoring CRC errors
>> release re-tuning
>>
>> But there is no wake-up function and the suspend path is using an unbalanced
>> mmc_sleep i.e. no corresponding wake up.
>>
>> So that leaves what is happening now i.e. a comment plus explicit
>> hold()/release() in _mmc_suspend() so that future changes to _mmc_suspend()
>> know to take mmc_sleep re-tuning requirements into account.
>
> Why all this complexity?
>
> mmc_power_off() is called in _mmc_suspend(), that will eventually
> disable re-tune. Thus re-tuning will be prevented for
> commands/requests during the system PM resume sequence, until the card
> has been fully re-initialized (and a tuning sequence done). Isn't that
> sufficient?

Yes my original patch did not have any of that complexity. I added it in
response to our discussions.

As you wrote, _mmc_suspend() does not need to do anything with retuning
because mmc_sleep() is followed by mmc_power_off().

The original patch added a comment to mmc_sleep() and that was all. That
would still be the best approach.