[PATCH v3 2/3] mmc: sdhci-of-dwcmshc: Add runtime PM support

[Ulf Hansson]

On Tue, 14 Feb 2023 at 04:36, Shawn Lin <shawn.lin at rock-chips.com> wrote:
>
> Hi Ulf,
>
> On 2023/2/14 7:45, Ulf Hansson wrote:
> > On Thu, 2 Feb 2023 at 01:35, Shawn Lin <shawn.lin at rock-chips.com> wrote:
> >>
> >> This patch adds runtime PM support.
> >>
> >> Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>
> >> ---
> >>
> >> Changes in v2: None
> >>
> >>   drivers/mmc/host/sdhci-of-dwcmshc.c | 51 ++++++++++++++++++++++++++++++++++++-
> >>   1 file changed, 50 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-of-dwcmshc.c
> >> index 46b1ce7..fc917ed 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>
> >>
> >> @@ -551,6 +552,13 @@ static int dwcmshc_probe(struct platform_device *pdev)
> >>          if (err)
> >>                  goto err_setup_host;
> >>
> >> +       pm_runtime_get_noresume(&pdev->dev);
> >> +       pm_runtime_set_active(&pdev->dev);
> >> +       pm_runtime_enable(&pdev->dev);
> >> +       pm_runtime_set_autosuspend_delay(&pdev->dev, 50);
> >> +       pm_runtime_use_autosuspend(&pdev->dev);
> >> +       pm_runtime_put_autosuspend(&pdev->dev);
> >> +
> >>          return 0;
> >>
> >>   err_setup_host:
> >> @@ -580,6 +588,11 @@ static int dwcmshc_remove(struct platform_device *pdev)
> >>          if (rk_priv)
> >>                  clk_bulk_disable_unprepare(RK35xx_MAX_CLKS,
> >>                                             rk_priv->rockchip_clks);
> >> +
> >> +       pm_runtime_get_sync(&pdev->dev);
> >> +       pm_runtime_disable(&pdev->dev);
> >> +       pm_runtime_put_noidle(&pdev->dev);
> >> +
> >>          sdhci_pltfm_free(pdev);
> >>
> >>          return 0;
> >> @@ -638,7 +651,43 @@ static int dwcmshc_resume(struct device *dev)
> >>   }
> >>   #endif
> >>
> >> -static SIMPLE_DEV_PM_OPS(dwcmshc_pmops, dwcmshc_suspend, dwcmshc_resume);
> >> +#ifdef CONFIG_PM
> >> +static int dwcmshc_runtime_suspend(struct device *dev)
> >> +{
> >> +       struct sdhci_host *host = dev_get_drvdata(dev);
> >> +       u16 data;
> >> +       int ret;
> >> +
> >> +       ret = sdhci_runtime_suspend_host(host);
> >> +       if (ret)
> >> +               return ret;
> >> +
> >> +       data = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
> >> +       data &= ~SDHCI_CLOCK_CARD_EN;
> >> +       sdhci_writew(host, data, SDHCI_CLOCK_CONTROL);
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static int dwcmshc_runtime_resume(struct device *dev)
> >> +{
> >> +       struct sdhci_host *host = dev_get_drvdata(dev);
> >> +       u16 data;
> >> +
> >> +       data = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
> >> +       data |= SDHCI_CLOCK_CARD_EN;
> >> +       sdhci_writew(host, data, SDHCI_CLOCK_CONTROL);
> >> +
> >> +       return sdhci_runtime_resume_host(host, 0);
> >> +}
> >> +#endif
> >> +
> >> +static const struct dev_pm_ops dwcmshc_pmops = {
> >> +       SET_SYSTEM_SLEEP_PM_OPS(dwcmshc_suspend,
> >> +                               dwcmshc_resume)
> >
> > I have looked at dwcmshc_suspend(), which calls sdhci_suspend_host().
> > As sdhci_suspend_host() will write to internal registers of the IP
> > block, it's recommended to make sure the device's runtime resumed
> > before doing that call. So that needs to be added along with $subject
> > patch.
> >
>
> Yep, let me add a check here.
>
> > There is also another option that may better for you, which is to use
> > the pm_runtime_force_suspend|resume() helpers. There should be plenty
> > of references to look at, but don't hesitate to ask around that, if
> > you need some more help to get that working.
>
> If I understand correctly,  pm_runtime_force_suspend|resume() helpers
> would use runtime PM ops for suspend/resume routine. In this case, the
> main issue is the handling of clock is quite different. In suspend we
> need to gate all clocks but in rpm case, it shouldn't.

I see, but let me then ask, what's the point of keeping the clocks
ungated at runtime suspend?

That sounds like wasting energy to me - but maybe there are good reasons for it?

[...]

Kind regards
Uffe