[PATCH 2/4] drm/uAPI: Add "active bpc" as feedback channel for "max bpc" drm property
Werner Sembach
wse at tuxedocomputers.com
Mon Jun 7 08:53:45 UTC 2021
Am 07.06.21 um 09:52 schrieb Pekka Paalanen:
> On Fri, 4 Jun 2021 19:17:21 +0200
> Werner Sembach <wse at 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 at 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
>
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