Re: [PATCH v6 1/2] drm: Add connector property to limit max bpc

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Sep 17, 2018 at 09:52:08PM -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)
> V5: Make the property per connector(Ville)
> V6: Compare the requested bpc to connector bpc(Daniel)
>     Move the attach_property function to core(Ville)
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Kishore Kadiyala <kishore.kadiyala@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> ---
>  drivers/gpu/drm/drm_atomic.c        | 24 ++++++++++++++++++++++++
>  drivers/gpu/drm/drm_atomic_helper.c |  4 ++++
>  drivers/gpu/drm/drm_atomic_uapi.c   |  4 ++++
>  drivers/gpu/drm/drm_connector.c     | 34 ++++++++++++++++++++++++++++++++++
>  include/drm/drm_connector.h         | 20 ++++++++++++++++++++
>  5 files changed, 86 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 7ada75919756..fa9996deb132 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -390,6 +390,7 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
>  {
>  	struct drm_crtc_state *crtc_state;
>  	struct drm_writeback_job *writeback_job = state->writeback_job;
> +	struct drm_display_info *info = &connector->display_info;
>  
>  	if ((connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK) || !writeback_job)
>  		return 0;
> @@ -400,6 +401,29 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
>  		return -EINVAL;
>  	}
>  
> +	if (connector->max_bpc_property) {
> +		if (info->bpc != 0 && info->bpc < state->max_requested_bpc) {
> +			/* Don't use an invalid EDID bpc value */
> +			DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] Clamping requested"
> +					 " display bpp (was %d) to EDID reported"
> +					 "max of %d\n", connector->base.id,
> +					 connector->name,
> +					 state->max_requested_bpc, info->bpc);
> +			state->max_bpc = info->bpc;
> +		} else if (info->bpc != 0) {
> +			state->max_bpc = state->max_requested_bpc;
> +		} else {
> +			/* Clamp bpc to 8 on screens witout EDID 1.4 */
> +			DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] Clamping requested"
> +					 " display bpp (was %d) to default limit"
> +					 " of 24\n", connector->base.id,
> +					 connector->name, state->max_requested_bpc);
> +			state->max_bpc = 8;
> +		}
> +	} else {
> +		state->max_bpc = info->bpc ? info->bpc : 8;
> +	}

Something like

max_bpc = info->bpc ?: 8;
if (max_bpc_prop)
	max_bpc = min(max_bpc, max_requested_bpc);

for short?

Not quite sure the 8bpc fallback should be here. Maybe it should be in
the edid code instead? Though I guess we want something for edidless
displays too so maybe this is fine.

> +
>  	if (state->crtc)
>  		crtc_state = drm_atomic_get_existing_crtc_state(state->state,
>  								state->crtc);
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 3cf1aa132778..d9ce8077fb6a 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -639,6 +639,10 @@ 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_requested_bpc !=
> +			    new_connector_state->max_requested_bpc)
> +				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 d5b7f315098c..86ac33922b09 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -740,6 +740,8 @@ 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 == connector->max_bpc_property) {
> +		state->max_requested_bpc = val;
>  	} else if (connector->funcs->atomic_set_property) {
>  		return connector->funcs->atomic_set_property(connector,
>  				state, property, val);
> @@ -804,6 +806,8 @@ 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 == connector->max_bpc_property) {
> +		*val = state->max_requested_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_connector.c b/drivers/gpu/drm/drm_connector.c
> index 1e40e5decbe9..06ad59222e03 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -1583,6 +1583,40 @@ void drm_connector_set_link_status_property(struct drm_connector *connector,
>  EXPORT_SYMBOL(drm_connector_set_link_status_property);
>  
>  /**
> + * drm_connector_attach_max_bpc_property - attach "max bpc" property
> + * @connector: connector to attach max bpc property on.
> + * @min: The minimum bit depth supported by the connector.
> + * @max: The maximum bit depth supported by the connector.
> + *
> + * This is used to add support for limiting the bit depth on a connector.
> + *
> + * Returns:
> + * Zero on success, negative errno on failure.
> + */
> +int drm_connector_attach_max_bpc_property(struct drm_connector *connector, int
> +					  min, int max)
> +{
> +	struct drm_device *dev = connector->dev;
> +	struct drm_property *prop;
> +
> +	prop = connector->max_bpc_property;
> +	if (prop == NULL) {
> +		prop = drm_property_create_range(dev, 0, "max bpc", min, max);
> +		if (!prop)
> +			return -ENOMEM;
> +
> +		connector->max_bpc_property = prop;
> +	}
> +
> +	drm_object_attach_property(&connector->base, prop, max);
> +	connector->state->max_requested_bpc = max;
> +
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_connector_attach_max_bpc_property);
> +
> +/**
>   * drm_connector_init_panel_orientation_property -
>   *	initialize the connecters panel_orientation property
>   * @connector: connector for which to init the panel-orientation property.
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 91a877fa00cb..d9c60fde5372 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -461,6 +461,18 @@ struct drm_connector_state {
>  	 * drm_writeback_signal_completion()
>  	 */
>  	struct drm_writeback_job *writeback_job;
> +
> +	/**
> +	 * @max_requested_bpc: Connector property to limit the maximum bit
> +	 * depth of the pixels.
> +	 */
> +	unsigned int max_requested_bpc;
> +
> +	/**
> +	 * @max_bpc: Connector max_bpc based on the requested max_bpc property
> +	 * and the connector bpc limitations obtained from edid.
> +	 */
> +	unsigned int max_bpc;

Could make both of these u8.

>  };
>  
>  /**
> @@ -924,6 +936,12 @@ struct drm_connector {
>  	 */
>  	struct drm_property_blob *path_blob_ptr;
>  
> +	/**
> +	 * @max_bpc_property: Default connector property for the max bpc to be
> +	 * driven out of the connector.
> +	 */
> +	struct drm_property *max_bpc_property;
> +
>  #define DRM_CONNECTOR_POLL_HPD (1 << 0)
>  #define DRM_CONNECTOR_POLL_CONNECT (1 << 1)
>  #define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2)
> @@ -1201,6 +1219,8 @@ void drm_connector_set_link_status_property(struct drm_connector *connector,
>  					    uint64_t link_status);
>  int drm_connector_init_panel_orientation_property(
>  	struct drm_connector *connector, int width, int height);
> +int drm_connector_attach_max_bpc_property(struct drm_connector *connector,
> +					  int min, int max);
>  
>  /**
>   * struct drm_tile_group - Tile group metadata
> -- 
> 2.9.3

-- 
Ville Syrjälä
Intel
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