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

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Date:   Wed, 16 Dec 2020 19:25:05 +0100
From:   Guido Günther <agx@...xcpu.org>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     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 Lucas,
On Wed, Dec 16, 2020 at 01:05:36PM +0100, Lucas Stach wrote:
> 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.

Thanks for confirming!

> 
> > 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?

pm_runtime_resume_and_get is a nice API addition indeed.

I added the error handling but opted to stay with `pm_runtime_get_sync`
in this case since the error path already has a pm_runtime_put() hence
avoiding another goto target.

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

Done.

Thanks for having a look!
 -- Guido

> 
> Regards,
> Lucas
>