Date:   Wed, 24 Jul 2019 10:21:56 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mmc: host: sdhci-sprd: Fix the incorrect soft reset
 operation when runtime resuming

On Tue, 23 Jul 2019 at 20:39, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Tue, 23 Jul 2019 at 05:05, Baolin Wang <baolin.wang@...aro.org> wrote:
> >
> > Hi Ulf,
> >
> > On Mon, 22 Jul 2019 at 19:54, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > >
> > > On Wed, 17 Jul 2019 at 04:29, Baolin Wang <baolin.wang@...aro.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.
>
> Thanks for clarifying, please update the changelog accordingly.

Sure, sorry for confusing.

>
> >
> > >
> > > >
> > > > 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.
>
> Aha, I didn't read the code carefully enough. Apologize for the noise.

No worries :)

> >
> > >
> > > > 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@...aro.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.
>
> Right, I see that now, thanks for clarifying.
>
> However, there are still some weird things going on in
> sdhci_runtime_resume_host(). Like why is host->ops->enable_dma()
> called first, directly from sdhci_runtime_resume_host(), then again in
> sdhci_do_reset(), after host->ops->reset() has been called. Looks like
> the first call to ->enable_dma() doesn't make sense?

I am mot sure, since our host did not supply enable_dma() operation.
This logic was used by some other hardware and worked well, I am not
sure if it can reveal some issues if we change the logic here.

Adrian, could you help to explain why we put enable_dma() in front of
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 understand, but perhaps it would become more clear if
> sdhci_runtime_resume_host() is re-factored a bit. Maybe the caller can
> give it some new parameter to let it decide if a SDHCI_RESET_ALL shall
> be done or not.

Yes, sounds reasonable, but need change other host drivers which
issued the sdhci_runtime_resume_host().

Adrian, if you also agree with Ulf's suggestion, then I will post new
patches to add a parameter to decide the reset mode. Thanks.

-- 
Baolin Wang
Best Regards

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