Re: [PATCH v4] mmc: host: sdhci-sprd: Fix the incorrect soft reset operation when runtime resuming

[Baolin Wang <baolin.wang@linaro.org>]

On Tue, 23 Jul 2019 at 11:21, Chunyan Zhang <zhang.lyra@gmail.com> wrote:
>
> On Tue, 23 Jul 2019 at 11:05, Baolin Wang <baolin.wang@linaro.org> wrote:
> >
> > Hi Ulf,
> >
> > On Mon, 22 Jul 2019 at 19:54, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > >
> > > On Wed, 17 Jul 2019 at 04:29, Baolin Wang <baolin.wang@linaro.org> wrote:
> > > >
> > > > In sdhci_runtime_resume_host() function, we will always do software reset
> > > > for all, which will cause Spreadtrum host controller work abnormally after
> > > > resuming.
> > >
> > > What does "software reset for all" means?
> >
> > The SD host controller specification defines 3 types software reset:
> > software reset for data line, software reset for command line and
> > software reset for all.
> > Software reset for all means this reset affects the entire Host
> > controller except for the card detection circuit.
> >
> > >
> > > >
> > > > Thus for Spreadtrum platform that will not power down the SD/eMMC card during
> > > > runtime suspend, we should not do software reset for all.
> > >
> > > Normally, sdhci hosts that enters runtime suspend doesn't power off
> > > the card (there are some exceptions like PCI variants).
> >
> > Yes, same as our controller.
> >
> > >
> > > So, what's so special here and how does the reset come into play? I
> > > don't see sdhci doing a reset in sdhci_runtime_suspend|resume_host()
> > > and nor doesn the callback from the sdhci-sprd.c variant doing it.
> >
> > In sdhci_runtime_resume_host(), it will issue sdhci_init(host, 0) to
> > issue software reset for all.
> >
> > >
> > > > To fix this
> > > > issue, adding a specific reset operation that adds one condition to validate
> > > > the power mode to decide if we can do software reset for all or just reset
> > > > command and data lines.
> > > >
> > > > Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
> > > > ---
> > > > Changess from v3:
> > > >  - Use ios.power_mode to validate if the card is power down or not.
> > > >
> > > > Changes from v2:
> > > >  - Simplify the sdhci_sprd_reset() by issuing sdhci_reset().
> > > >
> > > > Changes from v1:
> > > >  - Add a specific reset operation instead of changing the core to avoid
> > > >  affecting other hardware.
> > > > ---
> > > >  drivers/mmc/host/sdhci-sprd.c |   19 ++++++++++++++++++-
> > > >  1 file changed, 18 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/mmc/host/sdhci-sprd.c b/drivers/mmc/host/sdhci-sprd.c
> > > > index 603a5d9..94f9726 100644
> > > > --- a/drivers/mmc/host/sdhci-sprd.c
> > > > +++ b/drivers/mmc/host/sdhci-sprd.c
> > > > @@ -373,6 +373,23 @@ static unsigned int sdhci_sprd_get_max_timeout_count(struct sdhci_host *host)
> > > >         return 1 << 31;
> > > >  }
> > > >
> > > > +static void sdhci_sprd_reset(struct sdhci_host *host, u8 mask)
> > > > +{
> > > > +       struct mmc_host *mmc = host->mmc;
> > > > +
> > > > +       /*
> > > > +        * When try to reset controller after runtime suspend, we should not
> > > > +        * reset for all if the SD/eMMC card is not power down, just reset
> > > > +        * command and data lines instead. Otherwise will meet some strange
> > > > +        * behaviors for Spreadtrum host controller.
> > > > +        */
> > > > +       if (host->runtime_suspended && (mask & SDHCI_RESET_ALL) &&
> > > > +           mmc->ios.power_mode == MMC_POWER_ON)
> > > > +               mask = SDHCI_RESET_CMD | SDHCI_RESET_DATA;
> > >
> > > Can sdhci_sprd_reset() be called when the host is runtime suspended?
> >
> > When host tries to runtime resume in sdhci_runtime_resume_host(), it
> > will call reset operation to do software reset.
> >
> > > That sounds like a bug to me, no?
> >
> > Since our controller will meet some strange behaviors if we do
> > software reset for all in sdhci_runtime_resume_host(), and try to
> > avoid changing the core logic of sdhci_runtime_resume_host() used by
> > other hardware controllers, thus I introduced a specific reset ops and
> > added some condition to make sure we just do software reset command
> > and data lines from runtime suspend state.
>
> I can make a verification on sprd's SC9863A, but that would take a
> little time, since I need to make sd card registered with sdhci-sprd.c
> first :)

Great, you can try it on your board. Thanks.

-- 
Baolin Wang
Best Regards