linux-kernel - Re: [PATCH v2 1/1] phy: fsl-imx8-mipi-dphy: Hook into runtime pm

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Message-ID: <ee22b072e0abe07559a3e6a63ccf6ece064a46cb.camel@pengutronix.de>
Date:   Wed, 16 Dec 2020 13:05:36 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Guido Günther <agx@...xcpu.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Robert Chiras <robert.chiras@....com>,
        Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/1] phy: fsl-imx8-mipi-dphy: Hook into runtime pm

Hi Guido,

this time hopefully with less broken quoting. My mailer is driving me
mad right now...

Am Mittwoch, dem 16.12.2020 um 12:27 +0100 schrieb Guido Günther:
> This allows us to shut down the mipi power domain on the imx8. The
> alternative would be to drop the dphy from the mipi power domain in the
> SOCs device tree and only have the DSI host controller visible there but
> since the PD is mostly about the PHY that would defeat it's purpose.

Adding RPM support is exactly the right course of action.

> This allows to shut off the power domain hen blanking the LCD panel:
> 
> pm_genpd_summary before:
> 
> domain                          status          slaves
>     /device                                             runtime status
> ----------------------------------------------------------------------
> mipi                            on
>     /devices/platform/soc@...oc@0:bus@...00000/30a00300.dphy  unsupported
>     /devices/platform/soc@...oc@0:bus@...00000/30a00000.mipi_dsi  suspended
> 
> after:
> 
> mipi                            off-0
>     /devices/platform/soc@...oc@0:bus@...00000/30a00300.dphy  suspended
>     /devices/platform/soc@...oc@0:bus@...00000/30a00000.mipi_dsi  suspended
> 
> Signed-off-by: Guido Günther <agx@...xcpu.org>
> ---
>  .../phy/freescale/phy-fsl-imx8-mipi-dphy.c    | 22 ++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/phy/freescale/phy-fsl-imx8-mipi-dphy.c b/drivers/phy/freescale/phy-fsl-imx8-mipi-dphy.c
> index a95572b397ca..34e2d801e520 100644
> --- a/drivers/phy/freescale/phy-fsl-imx8-mipi-dphy.c
> +++ b/drivers/phy/freescale/phy-fsl-imx8-mipi-dphy.c
> @@ -14,6 +14,7 @@
>  #include <linux/of_platform.h>
>  #include <linux/phy/phy.h>
>  #include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
>  #include <linux/regmap.h>
>  
>  /* DPHY registers */
> @@ -93,6 +94,7 @@ struct mixel_dphy_cfg {
>  };
>  
>  struct mixel_dphy_priv {
> +	struct device *dev;
>  	struct mixel_dphy_cfg cfg;
>  	struct regmap *regmap;
>  	struct clk *phy_ref_clk;
> @@ -382,6 +384,7 @@ static int mixel_dphy_power_on(struct phy *phy)
>  	ret = clk_prepare_enable(priv->phy_ref_clk);
>  	if (ret < 0)
>  		return ret;
> +	pm_runtime_get_sync(priv->dev);
>  

This call can fail and will leave you with an elevated rpm refcount.
Better use the new pm_runtime_resume_and_get to avoid this issue? 

Nitpick: I would add a blank line before the call.

Regards,
Lucas