Re: [PATCH 2/4] drm/uAPI: Add "active bpc" as feedback channel for "max bpc" drm property

[Werner Sembach <wse@tuxedocomputers.com>]

[-- Attachment #1: Type: text/plain, Size: 6584 bytes --]


Am 07.06.21 um 09:52 schrieb Pekka Paalanen:
> On Fri,  4 Jun 2021 19:17:21 +0200
> Werner Sembach <wse@tuxedocomputers.com> wrote:
>
>> Add a new general drm property "active bpc" which can be used by graphic drivers
>> to report the applied bit depth per pixel back to userspace.
>>
>> While "max bpc" can be used to change the color depth, there was no way to check
>> which one actually got used. While in theory the driver chooses the best/highest
>> color depth within the max bpc setting a user might not be fully aware what his
>> hardware is or isn't capable off. This is meant as a quick way to double check
>> the setup.
>>
>> In the future, automatic color calibration for screens might also depend on this
>> information available.
>>
>> Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
>> ---
>>   drivers/gpu/drm/drm_atomic_uapi.c |  2 ++
>>   drivers/gpu/drm/drm_connector.c   | 40 +++++++++++++++++++++++++++++++
>>   include/drm/drm_connector.h       | 15 ++++++++++++
>>   3 files changed, 57 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
>> index 268bb69c2e2f..7ae4e40936b5 100644
>> --- a/drivers/gpu/drm/drm_atomic_uapi.c
>> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
>> @@ -873,6 +873,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
>>   		*val = 0;
>>   	} else if (property == connector->max_bpc_property) {
>>   		*val = state->max_requested_bpc;
>> +	} else if (property == connector->active_bpc_property) {
>> +		*val = state->active_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 7631f76e7f34..5f42a5be5822 100644
>> --- a/drivers/gpu/drm/drm_connector.c
>> +++ b/drivers/gpu/drm/drm_connector.c
>> @@ -1195,6 +1195,13 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
>>    *	drm_connector_attach_max_bpc_property() to create and attach the
>>    *	property to the connector during initialization.
>>    *
>> + * active bpc:
>> + *	This read-only range property is used by userspace check the bit depth
>> + *	actually applied by the GPU driver after evaluation all hardware
>> + *	capabilities and max bpc. Drivers to use the function
>> + *	drm_connector_attach_active_bpc_property() to create and attach the
>> + *	property to the connector during initialization.
>> + *
> Hi Werner,
>
> the idea looks good to me, but the above doc could be a little more
> fluent. May I suggest something like:
>
> 	This read-only range property tells userspace the pixel color
> 	bit depth 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, and
> 	the "max bpc" property. Drivers shall use
> 	drm_connector_attach_active_bpc_property() to install this
> 	property.
>
> There should also be something said about dithering done by the display
> engine (not monitor), but I'm not sure how that should be worded. It
> may also depend on if and how userspace can know about dithering. So if
> a dithering related property is added later, maybe add a note here too
> in that patch.
For this, and the DSC that Ville Syrjälä mentioned, I guess "the same 
behavior as max bpc" would be the most intuitive. But I don't know what 
that is and it's also not mentioned in the documentation.
>
>
> Thanks,
> pq
>
>
>>    * Connectors also have one standardized atomic property:
>>    *
>>    * CRTC_ID:
>> @@ -2150,6 +2157,39 @@ int drm_connector_attach_max_bpc_property(struct drm_connector *connector,
>>   }
>>   EXPORT_SYMBOL(drm_connector_attach_max_bpc_property);
>>   
>> +/**
>> + * drm_connector_attach_active_bpc_property - attach "active bpc" property
>> + * @connector: connector to attach active 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 check the applied bit depth on a connector.
>> + *
>> + * Returns:
>> + * Zero on success, negative errno on failure.
>> + */
>> +int drm_connector_attach_active_bpc_property(struct drm_connector *connector,
>> +					  int min, int max)
>> +{
>> +	struct drm_device *dev = connector->dev;
>> +	struct drm_property *prop;
>> +
>> +	prop = connector->active_bpc_property;
>> +	if (!prop) {
>> +		prop = drm_property_create_range(dev, 0, "active bpc", min, max);
>> +		if (!prop)
>> +			return -ENOMEM;
>> +
>> +		connector->active_bpc_property = prop;
>> +	}
>> +
>> +	drm_object_attach_property(&connector->base, prop, 0);
>> +	connector->state->active_bpc = 0;
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL(drm_connector_attach_active_bpc_property);
>> +
>>   /**
>>    * drm_connector_set_vrr_capable_property - sets the variable refresh rate
>>    * capable property for a connector
>> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
>> index 1922b278ffad..c58cba2b6afe 100644
>> --- a/include/drm/drm_connector.h
>> +++ b/include/drm/drm_connector.h
>> @@ -781,6 +781,13 @@ struct drm_connector_state {
>>   	 */
>>   	u8 max_bpc;
>>   
>> +	/**
>> +	 * @active_bpc: Read only property set by the GPU driver to the actually
>> +	 * applied bit depth of the pixels after evaluating all hardware
>> +	 * limitations.
>> +	 */
>> +	u8 active_bpc;
>> +
>>   	/**
>>   	 * @hdr_output_metadata:
>>   	 * DRM blob property for HDR output metadata
>> @@ -1380,6 +1387,12 @@ struct drm_connector {
>>   	 */
>>   	struct drm_property *max_bpc_property;
>>   
>> +	/**
>> +	 * @active_bpc_property: Default connector property for the active bpc
>> +	 * to be driven out of the connector.
>> +	 */
>> +	struct drm_property *active_bpc_property;
>> +
>>   #define DRM_CONNECTOR_POLL_HPD (1 << 0)
>>   #define DRM_CONNECTOR_POLL_CONNECT (1 << 1)
>>   #define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2)
>> @@ -1698,6 +1711,8 @@ int drm_connector_set_panel_orientation_with_quirk(
>>   	int width, int height);
>>   int drm_connector_attach_max_bpc_property(struct drm_connector *connector,
>>   					  int min, int max);
>> +int drm_connector_attach_active_bpc_property(struct drm_connector *connector,
>> +					  int min, int max);
>>   
>>   /**
>>    * struct drm_tile_group - Tile group metadata
>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx

[-- Attachment #2: Type: text/html, Size: 7429 bytes --]