linux-kernel - Re: [PATCH v3 1/2] drm/msm/dp: Add support for determining the eDP/DP mode from DT

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Message-ID: <Zf2avBOq5hM13nQy@linaro.org>
Date: Fri, 22 Mar 2024 16:50:36 +0200
From: Abel Vesa <abel.vesa@...aro.org>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Rob Clark <robdclark@...il.com>,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Kuogee Hsieh <quic_khsieh@...cinc.com>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Johan Hovold <johan@...nel.org>, linux-arm-msm@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] drm/msm/dp: Add support for determining the
 eDP/DP mode from DT

On 24-03-22 09:30:21, Bjorn Andersson wrote:
> On Fri, Mar 22, 2024 at 03:22:22PM +0200, Abel Vesa wrote:
> > Instead of relying on different compatibles for eDP and DP, lookup
> > the panel node in devicetree to figure out the connector type and
> > then pass on that information to the PHY. External DP is not described
> > in DT, therefore, assume it's eDP if panel node is present.
> > 
> > Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> > ---
> >  drivers/gpu/drm/msm/dp/dp_display.c | 43 +++++++++++++++++++++++++++++++++----
> >  1 file changed, 39 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index c4cb82af5c2f..c9763f77c832 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -726,6 +726,14 @@ static int dp_init_sub_modules(struct dp_display_private *dp)
> >  	if (IS_ERR(phy))
> >  		return PTR_ERR(phy);
> >  
> > +	rc = phy_set_mode_ext(phy, PHY_MODE_DP,
> > +			      dp->dp_display.is_edp ? PHY_SUBMODE_EDP : PHY_SUBMODE_DP);
> > +	if (rc) {
> > +		DRM_ERROR("failed to set phy submode, rc = %d\n", rc);
> > +		dp->catalog = NULL;
> > +		goto error;
> > +	}
> > +
> >  	dp->catalog = dp_catalog_get(dev);
> >  	if (IS_ERR(dp->catalog)) {
> >  		rc = PTR_ERR(dp->catalog);
> > @@ -734,9 +742,7 @@ static int dp_init_sub_modules(struct dp_display_private *dp)
> >  		goto error;
> >  	}
> >  
> > -	dp->aux = dp_aux_get(dev, dp->catalog,
> > -			     phy,
> > -			     dp->dp_display.is_edp);
> > +	dp->aux = dp_aux_get(dev, dp->catalog, phy, dp->dp_display.is_edp);
> >  	if (IS_ERR(dp->aux)) {
> >  		rc = PTR_ERR(dp->aux);
> >  		DRM_ERROR("failed to initialize aux, rc = %d\n", rc);
> > @@ -1241,6 +1247,35 @@ static int dp_auxbus_done_probe(struct drm_dp_aux *aux)
> >  	return dp_display_probe_tail(aux->dev);
> >  }
> >  
> > +static int dp_display_get_connector_type(struct platform_device *pdev,
> > +					 const struct msm_dp_desc *desc)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct device_node *aux_bus;
> > +	struct device_node *panel;
> > +	int ret = DRM_MODE_CONNECTOR_DisplayPort;
> > +
> > +	/* legacy platforms specify connector type in match data */
> > +	if (desc->connector_type == DRM_MODE_CONNECTOR_eDP ||
> > +		desc->connector_type == DRM_MODE_CONNECTOR_DisplayPort)
> > +		return desc->connector_type;
> > +
> > +	aux_bus = of_get_child_by_name(dev->of_node, "aux-bus");
> > +	if (!aux_bus)
> > +		goto out;
> 
> My compiler warns that if we take this code path, then you will
> of_node_put(<uninitialized panel>) below.
> 
> > +
> > +	panel = of_get_child_by_name(aux_bus, "panel");
> > +	if (!panel)
> > +		goto out;
> > +
> > +	ret = DRM_MODE_CONNECTOR_eDP;
> 
> My brain read this function as:
> check something
> if (error)
>   bailout!
> 
> check something
> if (error)
>   bailout!
> 
> ret should be edp
> 
> I then have to scan the code again to figure out what ret is otherwise,
> and convince myself that the error path is never an error, but a totally
> normal case.
> 
> 
> If you instead rely on the fact that both of_get_child_by_name() and
> of_node_put() can be passed NULL, you can write this as:
> 
> static int fn(..) {
>   aux_bus = of_get_child_by_name(dev->of_node, "aux-bus");
>   panel = of_get_child_by_name(aux_bus, "panel");
> 
>   if (panel)
>     connector_type = DRM_MODE_CONNECTOR_eDP;
>   else
>     connector_type = DRM_MODE_CONNECTOR_DisplayPort;
> 
>   of_node_put(panel);
>   of_node_put(aux_bus);
> 
>   return connector_type;
> }
> 
> Much easier to read, and you don't even have to zero-initialize panel to
> avoid that compiler warning.
> 

Fair enough, will do that instead.

> Regards,
> Bjorn
> 
> > +
> > +out:
> > +	of_node_put(panel);
> > +	of_node_put(aux_bus);
> > +	return ret;
> > +}
> > +
> >  static int dp_display_probe(struct platform_device *pdev)
> >  {
> >  	int rc = 0;
> > @@ -1263,7 +1298,7 @@ static int dp_display_probe(struct platform_device *pdev)
> >  	dp->dp_display.pdev = pdev;
> >  	dp->name = "drm_dp";
> >  	dp->id = desc->id;
> > -	dp->dp_display.connector_type = desc->connector_type;
> > +	dp->dp_display.connector_type = dp_display_get_connector_type(pdev, desc);
> >  	dp->wide_bus_supported = desc->wide_bus_supported;
> >  	dp->dp_display.is_edp =
> >  		(dp->dp_display.connector_type == DRM_MODE_CONNECTOR_eDP);
> > 
> > -- 
> > 2.34.1
> >