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

[Ulf Hansson]

On Fri, 11 Aug 2023 at 07:57, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 10/08/23 19:34, Ulf Hansson wrote:
> > On Thu, 10 Aug 2023 at 14:44, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
> >>
> >> On 10/08/23 13:21, Ulf Hansson wrote:
> >>> 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?
> >>
> >> I am OK with drivers that just want to use runtime PM to turn off a
> >> functional clock.  sdhci-tegra.c is also doing that although using the
> >> clock framework.
> >
> > Yes, I agree. At least this works for SoC specific drivers.
> >
> >>
> >> Certainly that approach assumes that the host controller's power state
> >> is not changed due to runtime PM.
> >>
> >> To ensure that the host controller is runtime resumed before calling
> >> sdhci_suspend_host(), we can just call pm_runtime_resume() I think.
> >
> > Yes, that was kind of what I proposed in the other thread as option 1)
> > (except for the replacement of pm_runtime_force_suspend|resume).
> >
> > Although, to be clear I would probably use pm_runtime_get_sync()
> > instead, to make sure the usage count is incremented too.
>
> In that case, a matching pm_runtime_put() is needed also at the
> end of the resume callback.

Yes, of course. Or depending if we are using the force_suspend|resume
helper, a pm_runtime_put_noidle is sufficient after
pm_runtime_force_suspend() has been called.

[...]

Kind regards
Uffe