Re: [PATCH v4 04/10] drm/bridge: Act on the DRM color format property

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

On Wednesday, 19 November 2025 05:32:46 Central European Standard Time Laurent Pinchart wrote:
> On Mon, Nov 17, 2025 at 08:11:48PM +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. Specifically, reject any output bus
> > formats that do not correspond to the requested color format.
> > 
> > Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> > ---
> >  drivers/gpu/drm/drm_bridge.c | 57 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 57 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > index 8f355df883d8..b7df5cbad832 100644
> > --- a/drivers/gpu/drm/drm_bridge.c
> > +++ b/drivers/gpu/drm/drm_bridge.c
> > @@ -1052,6 +1052,59 @@ 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_color_format fmt)
> > +{
> > +	if (bus_fmt == MEDIA_BUS_FMT_FIXED)
> > +		return true;
> > +
> > +	switch (fmt) {
> > +	case DRM_COLOR_FORMAT_NONE:
> > +	case DRM_COLOR_FORMAT_AUTO:
> > +		return true;
> > +	case DRM_COLOR_FORMAT_RGB444:
> > +		switch (bus_fmt) {
> > +		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 true;
> > +		default:
> > +			return false;
> > +		}
> > +	case DRM_COLOR_FORMAT_YCBCR444:
> > +		switch (bus_fmt) {
> > +		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 true;
> > +		default:
> > +			return false;
> > +		}
> > +	case DRM_COLOR_FORMAT_YCBCR422:
> > +		switch (bus_fmt) {
> > +		case MEDIA_BUS_FMT_UYVY8_1X16:
> > +		case MEDIA_BUS_FMT_UYVY10_1X20:
> > +		case MEDIA_BUS_FMT_UYVY12_1X24:
> > +			return true;
> > +		default:
> > +			return false;
> > +		}
> > +	case DRM_COLOR_FORMAT_YCBCR420:
> > +		switch (bus_fmt) {
> > +		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 true;
> > +		default:
> > +			return false;
> > +		}
> > +	}
> 
> I'd find this more readable:
> 
> 	if (fmt == DRM_COLOR_FORMAT_NONE || fmt == DRM_COLOR_FORMAT_AUTO)
> 		return true;
> 
> 	switch (bus_fmt) {
> 	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_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_COLOR_FORMAT_YCBCR444;
> 
> 	case MEDIA_BUS_FMT_UYVY8_1X16:
> 	case MEDIA_BUS_FMT_UYVY10_1X20:
> 	case MEDIA_BUS_FMT_UYVY12_1X24:
> 		return fmt == DRM_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_COLOR_FORMAT_YCBCR420;
> 
> 	default:
> 		return false;
> 	}
> 
> but it could be a matter for personal preference ?

I agree, that is nicer.

> 
> I'm also a bit concerned about the 
> 
> 	if (fmt == DRM_COLOR_FORMAT_NONE || fmt == DRM_COLOR_FORMAT_AUTO)
> 
> test. What's the difference between NONE and AUTO ? Is it meaningful, or
> should the two enumerators be merged into a single one ?

I've noticed that as well but didn't act on it before sending out v4.
I think we should try to make them the same yes. I don't see a valid
reason why anything would ever set "NONE" when it means "AUTO". If
there is a non-AUTO "NONE" case to describe an invalid format, then
this code is wrong anyways. I'll do some digging.

> > +
> > +	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.
> > @@ -1137,6 +1190,10 @@ drm_atomic_bridge_chain_select_bus_fmts(struct drm_bridge *bridge,
> >  	}
> >  
> >  	for (i = 0; i < num_out_bus_fmts; i++) {
> > +		if (!bus_format_is_color_fmt(out_bus_fmts[i], conn_state->color_format)) {
> > +			ret = -ENOTSUPP;
> > +			continue;
> > +		}
> >  		ret = select_bus_fmt_recursive(bridge, last_bridge, crtc_state,
> >  					       conn_state, out_bus_fmts[i]);
> >  		if (ret != -ENOTSUPP)
> 
>