[PATCH v4 1/2] drm: Add connector property to limit max bpc

[Ville Syrjälä]

On Thu, Aug 30, 2018 at 08:06:48AM -0700, Radhakrishna Sripada wrote:
> At times 12bpc HDMI cannot be driven due to faulty cables, dongles
> level shifters etc. To workaround them we may need to drive the output
> at a lower bpc. Currently the user space does not have a way to limit
> the bpc. The default bpc to be programmed is decided by the driver and
> is run against connector limitations.
> 
> Creating a new connector property "max bpc" in order to limit the bpc.
> xrandr can make use of this connector property to make sure that bpc does
> not exceed the configured value. This property can be used by userspace to
> set the bpc.
> 
> V2: Initialize max_bpc to satisfy kms_properties
> V3: Move the property to drm_connector
> V4: Split drm and i915 components(Ville)
> 
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Kishore Kadiyala <kishore.kadiyala at intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Manasi Navare <manasi.d.navare at intel.com>
> Cc: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
> ---
>  drivers/gpu/drm/drm_atomic.c        | 4 ++++
>  drivers/gpu/drm/drm_atomic_helper.c | 4 ++++
>  include/drm/drm_connector.h         | 6 ++++++
>  include/drm/drm_mode_config.h       | 5 +++++
>  4 files changed, 19 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index d0478abc01bd..4e352fc1f0a0 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1420,6 +1420,8 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
>  
>  		return set_out_fence_for_connector(state->state, connector,
>  						   fence_ptr);
> +	} else if (property == config->max_bpc_property) {
> +		state->max_bpc = val;
>  	} else if (connector->funcs->atomic_set_property) {
>  		return connector->funcs->atomic_set_property(connector,
>  				state, property, val);
> @@ -1515,6 +1517,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
>  		*val = 0;
>  	} else if (property == config->writeback_out_fence_ptr_property) {
>  		*val = 0;
> +	} else if (property == config->max_bpc_property) {
> +		*val = state->max_bpc;
>  	} else if (connector->funcs->atomic_get_property) {
>  		return connector->funcs->atomic_get_property(connector,
>  				state, property, val);
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 2c23a48482da..7f763650a623 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -638,6 +638,10 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
>  			if (old_connector_state->link_status !=
>  			    new_connector_state->link_status)
>  				new_crtc_state->connectors_changed = true;
> +
> +			if (old_connector_state->max_bpc !=
> +			    new_connector_state->max_bpc)
> +				new_crtc_state->connectors_changed = true;
>  		}
>  
>  		if (funcs->atomic_check)
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 97ea41dc678f..fc11f40aae51 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -460,6 +460,12 @@ struct drm_connector_state {
>  	 * drm_writeback_signal_completion()
>  	 */
>  	struct drm_writeback_job *writeback_job;
> +
> +	/**
> +	 * @max_bpc: Connector property to limit the maximum bit depth of
> +	 * the pixels.
> +	 */
> +	unsigned int max_bpc;
>  };
>  
>  /**
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index a0b202e1d69a..b9cd7a73b244 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -562,6 +562,11 @@ struct drm_mode_config {
>  	 */
>  	struct drm_property *link_status_property;
>  	/**
> +	 * @max_bpc_property: Default connector property for the max bpc to be
> +	 * driven out of the connector.
> +	 */
> +	struct drm_property *max_bpc_property;

If we want the exposed limits to be accurate this needs to be
per-connector. The other option of course is to just expose the
global min-max range for the entire device.

The way you wrote the i915 bits suggest you wanted to go for
the per-connector apporach instead.

> +	/**
>  	 * @plane_type_property: Default plane property to differentiate
>  	 * CURSOR, PRIMARY and OVERLAY legacy uses of planes.
>  	 */
> -- 
> 2.9.3

-- 
Ville Syrjälä
Intel