RE: [PATCH v5] mmc: sdhci-of-dwcmshc: Add runtime PM operations

[Liming Sun]

> -----Original Message-----
> From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Sent: Tuesday, August 1, 2023 11:37 AM
> To: Liming Sun <limings@xxxxxxxxxx>; Ulf Hansson <ulf.hansson@xxxxxxxxxx>;
> David Thompson <davthompson@xxxxxxxxxx>; Shawn Lin <shawn.lin@rock-
> chips.com>
> Cc: linux-mmc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5] mmc: sdhci-of-dwcmshc: Add runtime PM operations
> 
> On 28/07/23 15:20, 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>
> > ---
> > 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 | 54
> ++++++++++++++++++++++++++++-
> >  1 file changed, 53 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-
> of-dwcmshc.c
> > index e68cd87998c8..5cee42d72257 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>
> >
> > @@ -559,6 +560,8 @@ static int dwcmshc_probe(struct platform_device
> *pdev)
> >  	if (err)
> >  		goto err_setup_host;
> >
> > +	devm_pm_runtime_enable(dev);
> 
> By default, runtime PM regards the device as not active, so
> typically drivers will use something like pm_runtime_set_active()
> prior to pm_runtime_enable(dev)
> 
> In fact it is better to enable before adding the host but
> increment the usage count to prevent runtime suspend.  That
> means adding some get/puts, ending up with something like:
> 
> +	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);
> 
> 	err = __sdhci_add_host(host);
> 	if (err)
> 		goto err_setup_host;
> 
> +	pm_runtime_put_sync(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);
> 	if (rk_priv)
> 		clk_bulk_disable_unprepare(RK35xx_MAX_CLKS,
> 					   rk_priv->rockchip_clks);
> free_pltfm:
> 	sdhci_pltfm_free(pdev);
> 	return err;
> 

Updated in v6.

> > +
> >  	return 0;
> >
> >  err_setup_host:
> > @@ -646,7 +649,56 @@ static int dwcmshc_resume(struct device *dev)
> >  }
> >  #endif
> >
> > -static SIMPLE_DEV_PM_OPS(dwcmshc_pmops, dwcmshc_suspend,
> dwcmshc_resume);
> > +#ifdef CONFIG_PM
> > +
> > +static void dwcmshc_enable_card_clk(struct sdhci_host *host)
> > +{
> > +	u16 ctrl;
> > +
> > +	ctrl = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
> 
> You could save an mmio write:
> 
> 	if (ctrl & SDHCI_CLOCK_INT_EN && !(ctrl & SDHCI_CLOCK_CARD_EN)) {
> 
> > +	ctrl |= SDHCI_CLOCK_CARD_EN;
> > +	sdhci_writew(host, ctrl, SDHCI_CLOCK_CONTROL);
> 
> 	}

Updated in v6.

> 
> > +}
> > +
> > +static void dwcmshc_disable_card_clk(struct sdhci_host *host)
> > +{
> > +	u16 ctrl;
> > +
> > +	ctrl = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
> 
> You could save an mmio write:
> 
> 	if (ctrl & SDHCI_CLOCK_CARD_EN) {
> 
> > +	ctrl &= ~SDHCI_CLOCK_CARD_EN;
> > +	sdhci_writew(host, ctrl, SDHCI_CLOCK_CONTROL);
> 
> 	}

Updated in v6.

> 
> > +}
> > +
> > +static int dwcmshc_runtime_suspend(struct device *dev)
> > +{
> > +	struct sdhci_host *host = dev_get_drvdata(dev);
> > +	int ret = 0;
> 
> ret doesn't need initialization

Updated in v6.

> 
> > +
> > +	ret = sdhci_runtime_suspend_host(host);
> 
> If you *only* want to disable the card clock, then
> it is probably not necessary to call sdhci_runtime_suspend_host()
> and sdhci_runtime_resume_host().
> 

If, only cares about the card clock. Tested and removed the 
sdhci_runtime_suspend_host() and sdhci_runtime_resume_host()
to keep it simple. 

> > +	if (!ret)
> > +		dwcmshc_disable_card_clk(host);
> > +
> > +	return ret;
> > +}
> > +
> > +static int dwcmshc_runtime_resume(struct device *dev)
> > +{
> > +	struct sdhci_host *host = dev_get_drvdata(dev);
> > +	int ret = 0;
> 
> ret isn't needed

Removed in v6.

> 
> > +
> > +	dwcmshc_enable_card_clk(host);
> > +	ret = sdhci_runtime_resume_host(host, 0);
> 
> just
> 	return sdhci_runtime_resume_host(host, 0);

Updated in v6.

> 
> > +
> > +	return ret;
> > +}
> > +
> > +#endif
> > +
> > +static const struct dev_pm_ops dwcmshc_pmops = {
> > +	SET_SYSTEM_SLEEP_PM_OPS(dwcmshc_suspend, dwcmshc_resume)
> 
> Typically you need a way to coordinate runtime PM and system PM, refer:
> 
> https://www.kernel.org/doc/html/latest/power/runtime_pm.html#runtime-
> pm-and-system-sleep

Thanks. Added pm_runtime_force_suspend() and
pm_runtime_force_resume() in the system sleep() 
and resume() function to make the two states consistent.

> 
> > +	SET_RUNTIME_PM_OPS(dwcmshc_runtime_suspend,
> > +			   dwcmshc_runtime_resume, NULL)
> > +};
> >
> >  static struct platform_driver sdhci_dwcmshc_driver = {
> >  	.driver	= {