Re: [PATCH v7] mmc: sdhci-of-dwcmshc: Add runtime PM operations

[Ulf Hansson]

On Thu, 10 Aug 2023 at 10:13, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 8/08/23 23:23, Liming Sun wrote:
> > This commit implements the runtime PM operations to disable eMMC
> > card clock when idle.
> >
> > Reviewed-by: David Thompson <davthompson@xxxxxxxxxx>
> > Signed-off-by: Liming Sun <limings@xxxxxxxxxx>
> > ---
> > v6->v7:
> >     - Address Ulf's comment;
> > v5->v6:
> >     - Address Adrian's more comments and add coordination between
> >       runtime PM and system PM;
> > v4->v5:
> >     - Address Adrian's comment to move the pm_enable to the end to
> >       avoid race;
> > v3->v4:
> >     - Fix compiling reported by 'kernel test robot';
> > v2->v3:
> >     - Revise the commit message;
> > v1->v2:
> >     Updates for comments from Ulf:
> >     - Make the runtime PM logic generic for sdhci-of-dwcmshc;
> > v1: Initial version.
> > ---
> >  drivers/mmc/host/sdhci-of-dwcmshc.c | 72 ++++++++++++++++++++++++++++-
> >  1 file changed, 70 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-of-dwcmshc.c
> > index e68cd87998c8..c8e145031429 100644
> > --- a/drivers/mmc/host/sdhci-of-dwcmshc.c
> > +++ b/drivers/mmc/host/sdhci-of-dwcmshc.c
> > @@ -15,6 +15,7 @@
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> >  #include <linux/of_device.h>
> > +#include <linux/pm_runtime.h>
> >  #include <linux/reset.h>
> >  #include <linux/sizes.h>
> >
> > @@ -548,9 +549,13 @@ static int dwcmshc_probe(struct platform_device *pdev)
> >
> >       host->mmc->caps |= MMC_CAP_WAIT_WHILE_BUSY;
> >
> > +     pm_runtime_get_noresume(dev);
> > +     pm_runtime_set_active(dev);
> > +     pm_runtime_enable(dev);
> > +
> >       err = sdhci_setup_host(host);
> >       if (err)
> > -             goto err_clk;
> > +             goto err_rpm;
> >
> >       if (rk_priv)
> >               dwcmshc_rk35xx_postinit(host, priv);
> > @@ -559,10 +564,15 @@ static int dwcmshc_probe(struct platform_device *pdev)
> >       if (err)
> >               goto err_setup_host;
> >
> > +     pm_runtime_put(dev);
> > +
> >       return 0;
> >
> >  err_setup_host:
> >       sdhci_cleanup_host(host);
> > +err_rpm:
> > +     pm_runtime_disable(dev);
> > +     pm_runtime_put_noidle(dev);
> >  err_clk:
> >       clk_disable_unprepare(pltfm_host->clk);
> >       clk_disable_unprepare(priv->bus_clk);
> > @@ -606,6 +616,12 @@ static int dwcmshc_suspend(struct device *dev)
> >       if (ret)
> >               return ret;
> >
> > +     ret = pm_runtime_force_suspend(dev);
> > +     if (ret) {
> > +             sdhci_resume_host(host);
> > +             return ret;
> > +     }
>
> Since you are only using the runtime PM callbacks to turn off the card
> clock via SDHCI_CLOCK_CONTROL, pm_runtime_force_suspend() and
> pm_runtime_force_resume() are not needed at all.

Right, it can be done without these too.

>
> sdhci_suspend_host() does not care if SDHCI_CLOCK_CARD_EN is on or off.
> (And you are disabling pltfm_host->clk and priv->bus_clk, so presumably
> the result is no clock either way)
>
> sdhci_resume_host() does not restore state unless
> SDHCI_QUIRK2_HOST_OFF_CARD_ON is used, it just resets, so the internal clock
> SDHCI_CLOCK_INT_EN is off which is consistent with either runtime suspended
> or runtime resumed.

Even if this may work, to me, it doesn't look like good practice for
how to use runtime PM in combination with system wide suspend/resume.

The point is, sdhci_suspend|resume_host() may end up reading/writing
to sdhci registers - and we should *not* allow that (because it may
not always work), unless the sdhci controller has been runtime resumed
first, right?

[...]

Kind regards
Uffe