Re: [PATCH RFC 2/4] mmc: sdio: Add capability to skip SDIO reset at scan

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

On 24/04/17 23:33, Ulf Hansson wrote:
> On 21 April 2017 at 12:08, Adrian Hunter <adrian.hunter@intel.com> wrote:
>> The SDIO card state might be being preserved during hibernation, for
>> example a SDIO wifi card supporting WOWLAN. That state will be lost if an
>> SDIO reset is done. One way to avoid that would be to build mmc core as a
>> module and simply not load it until after attempting to restore the
>> hibernation image. However that won't work if the hibernation image is
>> stored on eMMC which, of course, requires mmc core.
> 
> I don't follow here. Are you saying the SDIO card is kept powered in
> hibernation, as to be able to support WOWLAN, right?

Yes

> 
> Then, it feels plain wrong the mmc_rescan() tries to re-initialize it.
> That should never happen, unless something is broken of course.

The thing to note about hibernation is that there is a regular boot in
between saving the hibernation image and restoring it again.  At boot time,
the kernel knows almost nothing about whether there is a hibernation image
and whether or not it will be restored.  Consequently it becomes difficult
to avoid mmc_rescan().  As mentioned above, we need mmc_rescan() to
initialize the eMMC so that the hibernation image can be read.

> 
> Kind regards
> Uffe
> 
>>
>> It is assumed on such systems that the platform will power cycle the SDIO
>> card or not as necessary so that the SDIO reset is not needed. Add a
>> capability flag to reflect that and use it to skip the SDIO reset at scan
>> time.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>> ---
>>  drivers/mmc/core/core.c  | 6 +++++-
>>  include/linux/mmc/host.h | 1 +
>>  2 files changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>> index 6987976252ad..178e23bf0c30 100644
>> --- a/drivers/mmc/core/core.c
>> +++ b/drivers/mmc/core/core.c
>> @@ -2639,8 +2639,12 @@ static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
>>          * if the card is being re-initialized, just send it.  CMD52
>>          * should be ignored by SD/eMMC cards.
>>          * Skip it if we already know that we do not support SDIO commands
>> +        * Also skip it if we know this host controller has a SDIO card that
>> +        * needs to be able to restore from hibernation without losing the card
>> +        * state e.g. an SDIO wifi card supporting WOWLAN.
>>          */
>> -       if (!(host->caps2 & MMC_CAP2_NO_SDIO))
>> +       if (!(host->caps2 & MMC_CAP2_NO_SDIO) &&
>> +           !(host->caps2 & MMC_CAP2_NO_SDIO_RESET))
>>                 sdio_reset(host);
>>
>>         mmc_go_idle(host);
>> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
>> index 78c544e296cd..187a7ba41364 100644
>> --- a/include/linux/mmc/host.h
>> +++ b/include/linux/mmc/host.h
>> @@ -281,6 +281,7 @@ struct mmc_host {
>>         u32                     caps2;          /* More host capabilities */
>>
>>  #define MMC_CAP2_BOOTPART_NOACC        (1 << 0)        /* Boot partition no access */
>> +#define MMC_CAP2_NO_SDIO_RESET (1 << 1)        /* Do not SDIO reset at scan */
>>  #define MMC_CAP2_FULL_PWR_CYCLE        (1 << 2)        /* Can do full power cycle */
>>  #define MMC_CAP2_HS200_1_8V_SDR        (1 << 5)        /* can support */
>>  #define MMC_CAP2_HS200_1_2V_SDR        (1 << 6)        /* can support */
>> --
>> 1.9.1
>>
>