Re: [PATCH 5/7] drm/uAPI: Add "preferred color format" drm property as setting for userspace

[Maxime Ripard]

Hi,

On Tue, Jan 09, 2024 at 06:11:02PM +0000, Andri Yngvason wrote:
> From: Werner Sembach <wse@xxxxxxxxxxxxxxxxxxx>
> 
> Add a new general drm property "preferred color format" which can be used
> by userspace to tell the graphic drivers to which color format to use.
> 
> Possible options are:
>     - auto (default/current behaviour)
>     - rgb
>     - ycbcr444
>     - ycbcr422 (not supported by both amdgpu and i915)
>     - ycbcr420
> 
> In theory the auto option should choose the best available option for the
> current setup, but because of bad internal conversion some monitors look
> better with rgb and some with ycbcr444.

I looked at the patch and I couldn't find what is supposed to happen if
you set it to something else than auto, and the driver can't match that.
Are we supposed to fallback to the "auto" behaviour, or are we suppose
to reject the mode entirely?

The combination with the active output format property suggests the
former, but we should document it explicitly.

> Also, because of bad shielded connectors and/or cables, it might be
> preferable to use the less bandwidth heavy ycbcr422 and ycbcr420 formats
> for a signal that is less deceptible to interference.
> 
> In the future, automatic color calibration for screens might also depend on
> this option being available.
> 
> Signed-off-by: Werner Sembach <wse@xxxxxxxxxxxxxxxxxxx>
> Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Signed-off-by: Andri Yngvason <andri@xxxxxxxxxxx>
> Tested-by: Andri Yngvason <andri@xxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c |  4 +++
>  drivers/gpu/drm/drm_atomic_uapi.c   |  4 +++
>  drivers/gpu/drm/drm_connector.c     | 50 ++++++++++++++++++++++++++++-
>  include/drm/drm_connector.h         | 17 ++++++++++
>  4 files changed, 74 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 68ffcc0b00dca..745a43d9c5da3 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -707,6 +707,10 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
>  			if (old_connector_state->max_requested_bpc !=
>  			    new_connector_state->max_requested_bpc)
>  				new_crtc_state->connectors_changed = true;
> +
> +			if (old_connector_state->preferred_color_format !=
> +			    new_connector_state->preferred_color_format)
> +				new_crtc_state->connectors_changed = true;
>  		}
>  
>  		if (funcs->atomic_check)
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index 98d3b10c08ae1..eba5dea1249e5 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -798,6 +798,8 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
>  		state->max_requested_bpc = val;
>  	} else if (property == connector->privacy_screen_sw_state_property) {
>  		state->privacy_screen_sw_state = val;
> +	} else if (property == connector->preferred_color_format_property) {
> +		state->preferred_color_format = val;
>  	} else if (connector->funcs->atomic_set_property) {
>  		return connector->funcs->atomic_set_property(connector,
>  				state, property, val);
> @@ -881,6 +883,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
>  		*val = state->max_requested_bpc;
>  	} else if (property == connector->privacy_screen_sw_state_property) {
>  		*val = state->privacy_screen_sw_state;
> +	} else if (property == connector->preferred_color_format_property) {
> +		*val = state->preferred_color_format;
>  	} else if (connector->funcs->atomic_get_property) {
>  		return connector->funcs->atomic_get_property(connector,
>  				state, property, val);
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 30d62e505d188..4de48a38792cf 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -1061,6 +1061,14 @@ static const struct drm_prop_enum_list drm_dp_subconnector_enum_list[] = {
>  	{ DRM_MODE_SUBCONNECTOR_Native,	     "Native"    }, /* DP */
>  };
>  
> +static const struct drm_prop_enum_list drm_preferred_color_format_enum_list[] = {
> +	{ 0, "auto" },
> +	{ DRM_COLOR_FORMAT_RGB444, "rgb" },
> +	{ DRM_COLOR_FORMAT_YCBCR444, "ycbcr444" },
> +	{ DRM_COLOR_FORMAT_YCBCR422, "ycbcr422" },
> +	{ DRM_COLOR_FORMAT_YCBCR420, "ycbcr420" },
> +};
> +
>  static const struct drm_prop_enum_list drm_active_color_format_enum_list[] = {
>  	{ 0, "not applicable" },
>  	{ DRM_COLOR_FORMAT_RGB444, "rgb" },
> @@ -1398,11 +1406,20 @@ static const u32 dp_colorspaces =
>   *	drm_connector_attach_max_bpc_property() to create and attach the
>   *	property to the connector during initialization.
>   *
> + * preferred color format:
> + *	This property is used by userspace to change the used color format. When
> + *	used the driver will use the selected format if valid for the hardware,
> + *	sink, and current resolution and refresh rate combination. Drivers to
> + *	use the function drm_connector_attach_preferred_color_format_property()
> + *	to create and attach the property to the connector during
> + *	initialization. Possible values are "auto", "rgb", "ycbcr444",
> + *	"ycbcr422", and "ycbcr420".
> + *
>   * active color format:
>   *	This read-only property tells userspace the color format actually used
>   *	by the hardware display engine "on the cable" on a connector. The chosen
>   *	value depends on hardware capabilities, both display engine and
> - *	connected monitor. Drivers shall use
> + *	connected monitor, and the "preferred color format". Drivers shall use
>   *	drm_connector_attach_active_color_format_property() to install this
>   *	property. Possible values are "not applicable", "rgb", "ycbcr444",
>   *	"ycbcr422", and "ycbcr420".
> @@ -2468,6 +2485,37 @@ int drm_connector_attach_max_bpc_property(struct drm_connector *connector,
>  }
>  EXPORT_SYMBOL(drm_connector_attach_max_bpc_property);
>  
> +/**
> + * drm_connector_attach_preferred_color_format_property - attach "preferred color format" property
> + * @connector: connector to attach preferred color format property on.
> + *
> + * This is used to add support for selecting a color format on a connector.
> + *
> + * Returns:
> + * Zero on success, negative errno on failure.
> + */
> +int drm_connector_attach_preferred_color_format_property(struct drm_connector *connector)
> +{
> +	struct drm_device *dev = connector->dev;
> +	struct drm_property *prop;
> +
> +	if (!connector->preferred_color_format_property) {
> +		prop = drm_property_create_enum(dev, 0, "preferred color format",
> +						drm_preferred_color_format_enum_list,
> +						ARRAY_SIZE(drm_preferred_color_format_enum_list));
> +		if (!prop)
> +			return -ENOMEM;
> +
> +		connector->preferred_color_format_property = prop;
> +	}
> +
> +	drm_object_attach_property(&connector->base, prop, 0);
> +	connector->state->preferred_color_format = 0;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_connector_attach_preferred_color_format_property);
> +
>  /**
>   * drm_connector_attach_active_color_format_property - attach "active color format" property
>   * @connector: connector to attach active color format property on.
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 9ae73cfdceeb1..d7bc54c8b42cb 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -1026,6 +1026,16 @@ struct drm_connector_state {
>  	 */
>  	enum drm_privacy_screen_status privacy_screen_sw_state;
>  
> +	/**
> +	 * preferred_color_format: Property set by userspace to tell the GPU

That's not the proper doc format, you're missing a @

Maxime

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