linux-kernel - Re: [PATCH] mmc: sdhci: Fix incorrect switch to HS mode

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Message-ID: <CAOGqxeUJD7eQxRnH1rep=m2+Ga5DDF=uWMsc_j2NZgC+EnZqsg@mail.gmail.com>
Date:   Thu, 19 Sep 2019 07:57:45 -0400
From:   Alan Cooper <alcooperx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH] mmc: sdhci: Fix incorrect switch to HS mode

This does correct the sequence of switching to HS400 but it might be
safest to just add this to the latest until it gets a little testing
to make sure it doesn't expose some bug in existing controllers.

Thanks
Al

On Tue, Sep 3, 2019 at 10:52 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Tue, 3 Sep 2019 at 13:51, Al Cooper <alcooperx@...il.com> wrote:
> >
> > When switching from any MMC speed mode that requires 1.8v
> > (HS200, HS400 and HS400ES) to High Speed (HS) mode, the system
> > ends up configured for SDR12 with a 50MHz clock which is an illegal
> > mode.
> >
> > This happens because the SDHCI_CTRL_VDD_180 bit in the
> > SDHCI_HOST_CONTROL2 register is left set and when this bit is
> > set, the speed mode is controlled by the SDHCI_CTRL_UHS field
> > in the SDHCI_HOST_CONTROL2 register. The SDHCI_CTRL_UHS field
> > will end up being set to 0 (SDR12) by sdhci_set_uhs_signaling()
> > because there is no UHS mode being set.
> >
> > The fix is to change sdhci_set_uhs_signaling() to set the
> > SDHCI_CTRL_UHS field to SDR25 (which is the same as HS) for
> > any switch to HS mode.
> >
> > This was found on a new eMMC controller that does strict checking
> > of the speed mode and the corresponding clock rate. It caused the
> > switch to HS400 mode to fail because part of the sequence to switch
> > to HS400 requires a switch from HS200 to HS before going to HS400.
> >
> > This fix was suggested by Adrian Hunter
> >
> > Signed-off-by: Al Cooper <alcooperx@...il.com>
>
> Should this be applied for fixes and tagged for stable you think?
>
> Kind regards
> Uffe
>
> > ---
> >  drivers/mmc/host/sdhci.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index 61d845fe0b97..068149640ecd 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -1858,7 +1858,9 @@ void sdhci_set_uhs_signaling(struct sdhci_host *host, unsigned timing)
> >                 ctrl_2 |= SDHCI_CTRL_UHS_SDR104;
> >         else if (timing == MMC_TIMING_UHS_SDR12)
> >                 ctrl_2 |= SDHCI_CTRL_UHS_SDR12;
> > -       else if (timing == MMC_TIMING_UHS_SDR25)
> > +       else if (timing == MMC_TIMING_SD_HS ||
> > +                timing == MMC_TIMING_MMC_HS ||
> > +                timing == MMC_TIMING_UHS_SDR25)
> >                 ctrl_2 |= SDHCI_CTRL_UHS_SDR25;
> >         else if (timing == MMC_TIMING_UHS_SDR50)
> >                 ctrl_2 |= SDHCI_CTRL_UHS_SDR50;
> > --
> > 2.17.1
> >