Re: [PATCH v9] mmc: sdhci-of-dwcmshc: Add runtime PM operations

[Ulf Hansson]

On Thu, 17 Aug 2023 at 18:22, Liming Sun <limings@xxxxxxxxxx> 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>
> ---
> v8->v9:
>     - Address Adrian's comment to do the pm_runtime_put() in
>       dwcmshc_resume() instead; Error path changes not included yet.
> v7->v8:
>     - Address Ulf's comment (option-1);
>     - Updates for Adrian's comment to remove the force_suspend/resume
>       in dwcmshc_resume()/dwcmshc_suspend(); Add comments for
>       dwcmshc_resume()/dwcmshc_suspend();
> 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 | 76 +++++++++++++++++++++++++++--
>  1 file changed, 72 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-of-dwcmshc.c
> index e68cd87998c8..3b40f55ce2a4 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);
> @@ -602,9 +612,13 @@ static int dwcmshc_suspend(struct device *dev)
>         struct rk35xx_priv *rk_priv = priv->priv;
>         int ret;
>
> +       pm_runtime_get_sync(dev);
> +
>         ret = sdhci_suspend_host(host);
> -       if (ret)
> +       if (ret) {
> +               pm_runtime_put(dev);
>                 return ret;
> +       }
>
>         clk_disable_unprepare(pltfm_host->clk);
>         if (!IS_ERR(priv->bus_clk))
> @@ -642,11 +656,65 @@ static int dwcmshc_resume(struct device *dev)
>                         return ret;
>         }
>
> -       return sdhci_resume_host(host);
> +       ret = sdhci_resume_host(host);
> +       if (ret)
> +               return ret;
> +
> +       pm_runtime_put(dev);

To simplify the error path, I would suggest that you move the call to
pm_runtime_put() to dwcmshc_suspend(). In fact what you need is just a
call to pm_runtime_put_noidle(), somewhere after the call to
pm_runtime_get_sync().

This is because runtime suspend is prevented by the PM core as it
bumps the usage count with a pm_runtime_get_noresume() in the
device_prepare() phase.

> +
> +       return 0;
>  }
>  #endif

[...]

Kind regards
Uffe