linux-kernel - Re: [PATCH v2 4/5] drm: bridge: lvds-encoder: allow specifying the input bus format

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Message-ID: <20180327102741.GN27746@w540>
Date:   Tue, 27 Mar 2018 12:27:41 +0200
From:   jacopo mondi <jacopo@...ndi.org>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 4/5] drm: bridge: lvds-encoder: allow specifying the
 input bus format

Hi Peter, Laurent,
   thanks for the patches,

On Mon, Mar 26, 2018 at 11:24:46PM +0200, Peter Rosin wrote:
> If the bridge changes the bus format, allow this to be described in
> the bridge, instead of providing false information about the bus
> format of the connector or panel.
>
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>  .../bindings/display/bridge/lvds-transmitter.txt   |  6 ++++++
>  drivers/gpu/drm/bridge/lvds-encoder.c              | 25 ++++++++++++++++++++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt b/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
> index 50220190c203..8d40a2069252 100644
> --- a/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
> +++ b/Documentation/devicetree/bindings/display/bridge/lvds-transmitter.txt
> @@ -30,6 +30,12 @@ Required properties:
>    device-specific version corresponding to the device first
>    followed by the generic version.
>
> +Optional properties:
> +
> +- interface-pix-fmt:
> +  List of valid input bus formats of the encoder. Recognized bus formats
> +  are listed in ../bus-format.txt
> +

This comments applies here and to [3/5] as well.

Are we sure we want the supported bridge input format defined in DT
bindings?

Again, I may be biased, but as I see this, each bridge driver should
list its supported formats with MEDIA_BUS_FMT_ fourcc codes and return
the currently 'active' one when requested by the preceding bridge.

I understand for this driver, being compatible with both a generic lvds
encoder and a specific chip, the supported input formats are
different, but I would have used the 'of_device_id.data' field for
this and leave this out from DT bindings.

This makes the translation routine here implemented not required if
I'm not wrong...

Thanks
   j

>  Required nodes:
>
>  This device has two video ports. Their connections are modeled using the OF
> diff --git a/drivers/gpu/drm/bridge/lvds-encoder.c b/drivers/gpu/drm/bridge/lvds-encoder.c
> index 75b0d3f6e4de..b78619b5560a 100644
> --- a/drivers/gpu/drm/bridge/lvds-encoder.c
> +++ b/drivers/gpu/drm/bridge/lvds-encoder.c
> @@ -9,6 +9,7 @@
>
>  #include <drm/drmP.h>
>  #include <drm/drm_bridge.h>
> +#include <drm/drm_of.h>
>  #include <drm/drm_panel.h>
>
>  #include <linux/of_graph.h>
> @@ -16,6 +17,8 @@
>  struct lvds_encoder {
>  	struct drm_bridge bridge;
>  	struct drm_bridge *panel_bridge;
> +	int num_bus_formats;
> +	u32 *bus_formats;
>  };
>
>  static int lvds_encoder_attach(struct drm_bridge *bridge)
> @@ -28,8 +31,22 @@ static int lvds_encoder_attach(struct drm_bridge *bridge)
>  				 bridge);
>  }
>
> +static int lvds_encoder_input_formats(struct drm_bridge *bridge,
> +				      const u32 **bus_formats)
> +{
> +	struct lvds_encoder *lvds_encoder = container_of(bridge,
> +							 struct lvds_encoder,
> +							 bridge);
> +
> +	if (lvds_encoder->num_bus_formats)
> +		*bus_formats = lvds_encoder->bus_formats;
> +
> +	return lvds_encoder->num_bus_formats;
> +}
> +
>  static struct drm_bridge_funcs funcs = {
>  	.attach = lvds_encoder_attach,
> +	.input_formats = lvds_encoder_input_formats,
>  };
>
>  static int lvds_encoder_probe(struct platform_device *pdev)
> @@ -39,6 +56,7 @@ static int lvds_encoder_probe(struct platform_device *pdev)
>  	struct device_node *panel_node;
>  	struct drm_panel *panel;
>  	struct lvds_encoder *lvds_encoder;
> +	int ret;
>
>  	lvds_encoder = devm_kzalloc(&pdev->dev, sizeof(*lvds_encoder),
>  				    GFP_KERNEL);
> @@ -79,6 +97,12 @@ static int lvds_encoder_probe(struct platform_device *pdev)
>  	if (IS_ERR(lvds_encoder->panel_bridge))
>  		return PTR_ERR(lvds_encoder->panel_bridge);
>
> +	ret = drm_of_bus_formats(pdev->dev.of_node, "interface-pix-fmt",
> +				 &lvds_encoder->bus_formats);
> +	if (ret < 0)
> +		return ret;
> +	lvds_encoder->num_bus_formats = ret;
> +
>  	/* The panel_bridge bridge is attached to the panel's of_node,
>  	 * but we need a bridge attached to our of_node for our user
>  	 * to look up.
> @@ -96,6 +120,7 @@ static int lvds_encoder_remove(struct platform_device *pdev)
>  {
>  	struct lvds_encoder *lvds_encoder = platform_get_drvdata(pdev);
>
> +	kfree(lvds_encoder->bus_formats);
>  	drm_bridge_remove(&lvds_encoder->bridge);
>
>  	return 0;
> --
> 2.11.0
>

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