Re: [PATCH v9 03/19] drm/bridge: Act on the DRM color format property

[Nicolas Frattaroli <nicolas.frattaroli@collabora.com>]

On Sunday, 1 March 2026 17:56:08 Central European Standard Time Dmitry Baryshkov wrote:
> On Fri, Feb 27, 2026 at 08:20:08PM +0100, Nicolas Frattaroli wrote:
> > The new DRM color format property allows userspace to request a specific
> > color format on a connector. In turn, this fills the connector state's
> > color_format member to switch color formats.
> > 
> > Make drm_bridges consider the color_format set in the connector state
> > during the atomic bridge check. For bridges that represent HDMI bridges,
> > rely on whatever format the HDMI logic set. Reject any output bus
> > formats that do not correspond to the requested color format.
> > 
> > Non-HDMI last bridges with DRM_CONNECTOR_COLOR_FORMAT_AUTO set will end
> > up choosing the first output format that functions to make a whole
> > recursive bridge chain format selection succeed.
> > 
> > Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> > ---
> >  drivers/gpu/drm/drm_bridge.c | 89 +++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 88 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > index 6d8947419940..5938fba0a983 100644
> > --- a/drivers/gpu/drm/drm_bridge.c
> > +++ b/drivers/gpu/drm/drm_bridge.c
> > @@ -1117,6 +1117,47 @@ static int select_bus_fmt_recursive(struct drm_bridge *first_bridge,
> >  	return ret;
> >  }
> >  
> > +static bool __pure bus_format_is_color_fmt(u32 bus_fmt, enum drm_connector_color_format fmt)
> > +{
> > +	if (fmt == DRM_CONNECTOR_COLOR_FORMAT_AUTO)
> > +		return true;
> > +
> > +	switch (bus_fmt) {
> > +	case MEDIA_BUS_FMT_FIXED:
> > +		return true;
> > +	case MEDIA_BUS_FMT_RGB888_1X24:
> > +	case MEDIA_BUS_FMT_RGB101010_1X30:
> > +	case MEDIA_BUS_FMT_RGB121212_1X36:
> > +	case MEDIA_BUS_FMT_RGB161616_1X48:
> > +		return fmt == DRM_CONNECTOR_COLOR_FORMAT_RGB444;
> > +	case MEDIA_BUS_FMT_YUV8_1X24:
> > +	case MEDIA_BUS_FMT_YUV10_1X30:
> > +	case MEDIA_BUS_FMT_YUV12_1X36:
> > +	case MEDIA_BUS_FMT_YUV16_1X48:
> > +		return fmt == DRM_CONNECTOR_COLOR_FORMAT_YCBCR444;
> > +	case MEDIA_BUS_FMT_UYVY8_1X16:
> > +	case MEDIA_BUS_FMT_VYUY8_1X16:
> > +	case MEDIA_BUS_FMT_YUYV8_1X16:
> > +	case MEDIA_BUS_FMT_YVYU8_1X16:
> > +	case MEDIA_BUS_FMT_UYVY10_1X20:
> > +	case MEDIA_BUS_FMT_YUYV10_1X20:
> > +	case MEDIA_BUS_FMT_VYUY10_1X20:
> > +	case MEDIA_BUS_FMT_YVYU10_1X20:
> > +	case MEDIA_BUS_FMT_UYVY12_1X24:
> > +	case MEDIA_BUS_FMT_VYUY12_1X24:
> > +	case MEDIA_BUS_FMT_YUYV12_1X24:
> > +	case MEDIA_BUS_FMT_YVYU12_1X24:
> > +		return fmt == DRM_CONNECTOR_COLOR_FORMAT_YCBCR422;
> > +	case MEDIA_BUS_FMT_UYYVYY8_0_5X24:
> > +	case MEDIA_BUS_FMT_UYYVYY10_0_5X30:
> > +	case MEDIA_BUS_FMT_UYYVYY12_0_5X36:
> > +	case MEDIA_BUS_FMT_UYYVYY16_0_5X48:
> > +		return fmt == DRM_CONNECTOR_COLOR_FORMAT_YCBCR420;
> > +	default:
> > +		return false;
> > +	}
> > +}
> > +
> >  /*
> >   * This function is called by &drm_atomic_bridge_chain_check() just before
> >   * calling &drm_bridge_funcs.atomic_check() on all elements of the chain.
> > @@ -1160,6 +1201,7 @@ drm_atomic_bridge_chain_select_bus_fmts(struct drm_bridge *bridge,
> >  	struct drm_encoder *encoder = bridge->encoder;
> >  	struct drm_bridge_state *last_bridge_state;
> >  	unsigned int i, num_out_bus_fmts = 0;
> > +	enum drm_connector_color_format fmt;
> >  	u32 *out_bus_fmts;
> >  	int ret = 0;
> >  
> > @@ -1201,13 +1243,58 @@ drm_atomic_bridge_chain_select_bus_fmts(struct drm_bridge *bridge,
> >  			out_bus_fmts[0] = MEDIA_BUS_FMT_FIXED;
> >  	}
> >  
> > +	/*
> > +	 * On HDMI connectors, use the output format chosen by whatever does the
> > +	 * HDMI logic. For everyone else, just trust that the bridge out_bus_fmts
> > +	 * are sorted by preference for %DRM_CONNECTOR_COLOR_FORMAT_AUTO, as
> > +	 * bus_format_is_color_fmt() always returns true for AUTO.
> > +	 */
> > +	if (last_bridge->ops & DRM_BRIDGE_OP_HDMI) {
> 
> This will break the logic if there is anything after the HDMI bridge.
> For example, if the board has hdmi-connector (yep, it's a bridge without
> DRM_BRIDGE_OP_HDMI, because HDMI connectors don't implement any of the
> HDMI functionality), then the function will go to the second clause.
> 
> This probably needs to be moved to drm_bridge_connector. There is is
> natural to check for bridge_connector->bridge_hdmi.

A few questions:
1. are all HDMI connectors drm_bridge_connectors? Or does the code need
   to handle two HDMI cases?
2. If by "This probably needs to be moved to drm_bridge_connector", do
   you mean the entire recursive bus format selection, or just a check
   for whether it's an HDMI connector that sets some flag on the
   drm_bridge?
3. I don't see any KUnit tests for drm_bridge_connector. Is adding those
   part of the requirements for getting this upstreamed?

Kind regards,
Nicolas Frattaroli

> 
> > +		drm_dbg_kms(last_bridge->dev,
> > +			    "HDMI bridge requests format %s\n",
> > +			    drm_hdmi_connector_get_output_format_name(
> > +				    conn_state->hdmi.output_format));
> > +		switch (conn_state->hdmi.output_format) {
> > +		case DRM_OUTPUT_COLOR_FORMAT_RGB444:
> > +			fmt = DRM_CONNECTOR_COLOR_FORMAT_RGB444;
> > +			break;
> > +		case DRM_OUTPUT_COLOR_FORMAT_YCBCR444:
> > +			fmt = DRM_CONNECTOR_COLOR_FORMAT_YCBCR444;
> > +			break;
> > +		case DRM_OUTPUT_COLOR_FORMAT_YCBCR422:
> > +			fmt = DRM_CONNECTOR_COLOR_FORMAT_YCBCR422;
> > +			break;
> > +		case DRM_OUTPUT_COLOR_FORMAT_YCBCR420:
> > +			fmt = DRM_CONNECTOR_COLOR_FORMAT_YCBCR420;
> > +			break;
> > +		default:
> > +			ret = -EINVAL;
> > +			goto out_free_bus_fmts;
> > +		}
> > +	} else {
> > +		fmt = conn_state->color_format;
> > +		drm_dbg_kms(last_bridge->dev, "Non-HDMI bridge requests format %d\n", fmt);
> > +	}
> > +
> >  	for (i = 0; i < num_out_bus_fmts; i++) {
> > +		if (!bus_format_is_color_fmt(out_bus_fmts[i], fmt)) {
> > +			drm_dbg_kms(last_bridge->dev,
> > +				    "Skipping bus format 0x%04x as it doesn't match format %d\n",
> > +				    out_bus_fmts[i], fmt);
> > +			ret = -ENOTSUPP;
> > +			continue;
> > +		}
> >  		ret = select_bus_fmt_recursive(bridge, last_bridge, crtc_state,
> >  					       conn_state, out_bus_fmts[i]);
> > -		if (ret != -ENOTSUPP)
> > +		if (ret != -ENOTSUPP) {
> > +			drm_dbg_kms(last_bridge->dev,
> > +				    "Found bridge chain ending with bus format 0x%04x\n",
> > +				    out_bus_fmts[i]);
> >  			break;
> > +		}
> >  	}
> >  
> > +out_free_bus_fmts:
> >  	kfree(out_bus_fmts);
> >  
> >  	return ret;
> > 
> 
>