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

Hi,

On Fri, Jun 04, 2021 at 07:17:21PM +0200, Werner Sembach 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.

Just a heads up, we'll need an open source project that has accepted it before merging it.

See https://www.kernel.org/doc/html/latest/gpu/drm-uapi.html#open-source-userspa...

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

^ display

Depending on the system, the display component might have a GPU attached or not, and the GPU might have a display component or not.

• • 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.
• • 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;

I guess we want to default to 8?

Maxime