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

[Ulf Hansson]

+ Rafael

On Wed, 15 Feb 2023 at 01:50, Shawn Lin <shawn.lin at rock-chips.com> wrote:
>
> Hi Ulf
>
> On 2023/2/14 18:41, Ulf Hansson wrote:
> > 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?
>
> The point to keep the clocks ungated at runtime suspend is that if they
> are gated,  the DLL would lost its locked state which causes retuning
> every time. It's quite painful for performance. However, if we just gate
> output clock to the device, the devices(basically I refer to eMMC) will
> get into power-save status by itself. That helps us too keep balance
> between power & performance during runtime. ：）

I see, thanks for clarifying! In principle your approach should work
fine, but it depends a bit on the platform/soc too.

I assume there could also be a PM domain attached to the mmc host
device, right? If such a PM domain gets powered off, wouldn't you need
to run a retuning sequence anyway?

FYI, I have heard about similar problems for devices before - and it's
been discussed too. In principle, it sounds to me that we have devices
that would benefit from using *multiple* idle states, rather than just
the one we have for runtime suspend and the one for system wide
suspend.

Kind regards
Uffe