Re: [PATCH V2] drm/bridge: lvds-codec: Add support for pixel data sampling edge select

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Marek,

(CC'ing Ron and the DT mailing list for the DT discussion)

On Mon, Mar 22, 2021 at 11:29:04AM +0100, Marek Vasut wrote:
> On 3/22/21 2:14 AM, Laurent Pinchart wrote:
> > Hi Marek,
> 
> Hi,
> 
> [...]
> 
> >> diff --git a/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml b/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml
> >> index e5e3c72630cf..399a6528780a 100644
> >> --- a/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml
> >> +++ b/Documentation/devicetree/bindings/display/bridge/lvds-codec.yaml
> >> @@ -74,6 +74,13 @@ properties:
> >>   
> >>       additionalProperties: false
> >>   
> >> +  pixelclk-active:
> >> +    description: |
> >> +      Data sampling on rising or falling edge.
> >> +      Use 0 to sample pixel data on rising edge and
> >> +      Use 1 to sample pixel data on falling edge and
> >> +    enum: [0, 1]
> > 
> > The idea is good, but instead of adding a custom property, how about
> > reusing the pclk-sample property defined in
> > ../../media/video-interfaces.yaml ?
> 
> Repeating myself from V1 discussion ... Either is fine by me, but I 
> think pixelclk-active, which comes from panel-timings.yaml is closer to 
> the video than multimedia bindings.

That's a good point. The part that bothers me a bit is that it would be
nice to define the property in a single YAML schema, referenced by
individual bindings. video-interfaces.yaml is there for that purpose. We
could do something similar on the display side, or consider the
pixelclk-active usage in panel-timings.yaml an exception that we can't
switch to video-interfaces.yaml as backward compatibility must be
preserved.

I don't have a too strong preference, whatever Rob prefers would be fine
with me.

> > The property is only valid for encoders, so I would at least mention
> > that in the description, or, better, handle this based on the compatible
> > string to allow validation.
> 
> How does that work in the Yaml file ?

Something along the lines of

if:
  not:
    properties:
      compatible:
        contains:
          const: lvds-encoder
then:
  properties:
    pixelclk-active: false

My YAML schema foo is a bit rusty though, I apologize if this doesn't
work as-is. There are lots of similar examples in DT bindings that
should hopefully be right :-)

> >> +
> >>     powerdown-gpios:
> >>       description:
> >>         The GPIO used to control the power down line of this device.
> >> diff --git a/drivers/gpu/drm/bridge/lvds-codec.c b/drivers/gpu/drm/bridge/lvds-codec.c
> >> index dcf579a4cf83..cab81ccd895d 100644
> >> --- a/drivers/gpu/drm/bridge/lvds-codec.c
> >> +++ b/drivers/gpu/drm/bridge/lvds-codec.c
> 
> [...]
> 
> >> @@ -126,6 +146,7 @@ static int lvds_codec_probe(struct platform_device *pdev)
> >>   	 */
> >>   	lvds_codec->bridge.of_node = dev->of_node;
> >>   	lvds_codec->bridge.funcs = &funcs;
> >> +	lvds_codec->bridge.timings = &lvds_codec->timings;
> >>   	drm_bridge_add(&lvds_codec->bridge);
> >>   
> >>   	platform_set_drvdata(pdev, lvds_codec);
> >> @@ -142,19 +163,20 @@ static int lvds_codec_remove(struct platform_device *pdev)
> >>   	return 0;
> >>   }
> >>   
> >> +static const struct lvds_codec_data decoder_data = {
> >> +	.connector_type = DRM_MODE_CONNECTOR_DPI,
> >> +	.is_encoder = false,
> > 
> > The two fields are a bit redundant, as the decoder is always
> > LVDS-to-DPI, and the encoder DPI-to-LVDS. I don't mind too much, but
> > maybe we could drop the connector_type field, and derive the connector
> > type from is_encoder ?
> 
> Or the other way around instead ? That is, if the connector_type is 
> LVDS, then it is encoder , otherwise its decoder ?

Either way works for me.

> > One may then say that we could drop the lvds_codec_data structure as it
> > contains a single field, but I foresee a need to have device-specific
> > timings at some point, so I think it's a good addition.
> 
> [...]

-- 
Regards,

Laurent Pinchart