Hi, On Fri, Oct 31, 2025 at 04:45:34PM -0400, Sasha McIntosh wrote: > [Why] > When playing HDR or WCG content, bandwidth constraints may force the > driver to downgrade to 6bpc, resulting in visual artifacts like banding. Bit confused by this. How exactly would they reach 6bpc? The lower limit seems to be 8 [1]. > > Userspace should be able to configure a minimum allowed bpc. > > [How] > Introduce the "min bpc" connector property so the user can limit the > minimum bpc. Mirror the "mac bpc" implementation.
[1] https://elixir.bootlin.com/linux/v6.18-rc4/source/drivers/gpu/drm/display/drm_hdmi_state_helper.c#L620 > > Signed-off-by: Sasha McIntosh <[email protected]> > --- > drivers/gpu/drm/drm_atomic.c | 12 +++++++++ > drivers/gpu/drm/drm_atomic_helper.c | 4 +++ > drivers/gpu/drm/drm_atomic_uapi.c | 4 +++ > drivers/gpu/drm/drm_connector.c | 41 +++++++++++++++++++++++++++++ > include/drm/drm_connector.h | 20 ++++++++++++++ > 5 files changed, 81 insertions(+) > > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c > index be2cb6e43cb0..f85ad9c55e69 100644 > --- a/drivers/gpu/drm/drm_atomic.c > +++ b/drivers/gpu/drm/drm_atomic.c > @@ -468,6 +468,17 @@ static int drm_atomic_connector_check(struct > drm_connector *connector, > state->max_bpc = info->bpc ? info->bpc : 8; > if (connector->max_bpc_property) > state->max_bpc = min(state->max_bpc, state->max_requested_bpc); > + if (connector->min_bpc_property) > + state->min_bpc = state->min_requested_bpc; > + if (connector->max_bpc_property && connector->min_bpc_property && > + state->max_requested_bpc < state->min_requested_bpc) { > + drm_dbg_atomic(connector->dev, > + "[CONNECTOR:%d:%s] max bpc %d < min bpc %d\n", > + connector->base.id, connector->name, > + state->max_requested_bpc, > + state->min_requested_bpc); > + return -EINVAL; > + } > > if ((connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK) || > !writeback_job) > return 0; > @@ -1195,6 +1206,7 @@ static void drm_atomic_connector_print_state(struct > drm_printer *p, > drm_printf(p, "\tinterlace_allowed=%d\n", connector->interlace_allowed); > drm_printf(p, "\tycbcr_420_allowed=%d\n", connector->ycbcr_420_allowed); > drm_printf(p, "\tmax_requested_bpc=%d\n", state->max_requested_bpc); > + drm_printf(p, "\tmin_requested_bpc=%d\n", state->min_requested_bpc); > drm_printf(p, "\tcolorspace=%s\n", > drm_get_colorspace_name(state->colorspace)); > > if (connector->connector_type == DRM_MODE_CONNECTOR_HDMIA || > diff --git a/drivers/gpu/drm/drm_atomic_helper.c > b/drivers/gpu/drm/drm_atomic_helper.c > index 5a473a274ff0..75659d46c6fe 100644 > --- a/drivers/gpu/drm/drm_atomic_helper.c > +++ b/drivers/gpu/drm/drm_atomic_helper.c > @@ -736,6 +736,10 @@ drm_atomic_helper_check_modeset(struct drm_device *dev, > if (old_connector_state->max_requested_bpc != > new_connector_state->max_requested_bpc) > new_crtc_state->connectors_changed = true; > + > + if (old_connector_state->min_requested_bpc != > + new_connector_state->min_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 85dbdaa4a2e2..f99649f9c51f 100644 > --- a/drivers/gpu/drm/drm_atomic_uapi.c > +++ b/drivers/gpu/drm/drm_atomic_uapi.c > @@ -776,6 +776,8 @@ static int drm_atomic_connector_set_property(struct > drm_connector *connector, > fence_ptr); > } else if (property == connector->max_bpc_property) { > state->max_requested_bpc = val; > + } else if (property == connector->min_bpc_property) { > + state->min_requested_bpc = val; > } else if (property == connector->privacy_screen_sw_state_property) { > state->privacy_screen_sw_state = val; > } else if (property == connector->broadcast_rgb_property) { > @@ -861,6 +863,8 @@ 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->min_bpc_property) { > + *val = state->min_requested_bpc; > } else if (property == connector->privacy_screen_sw_state_property) { > *val = state->privacy_screen_sw_state; > } else if (property == connector->broadcast_rgb_property) { > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c > index 272d6254ea47..2d9cfd4f5118 100644 > --- a/drivers/gpu/drm/drm_connector.c > +++ b/drivers/gpu/drm/drm_connector.c > @@ -1699,6 +1699,13 @@ > EXPORT_SYMBOL(drm_hdmi_connector_get_output_format_name); > * drm_connector_attach_max_bpc_property() to create and attach the > * property to the connector during initialization. > * > + * min bpc: > + * This range property is used by userspace to set a lower bound for the > bit > + * depth. When used the driver would set the bpc in accordance with the > + * valid range supported by the hardware and sink. Drivers to use the > function > + * drm_connector_attach_min_bpc_property() to create and attach the > + * property to the connector during initialization. > + * > * Connectors also have one standardized atomic property: > * > * CRTC_ID: > @@ -2845,6 +2852,40 @@ int drm_connector_attach_max_bpc_property(struct > drm_connector *connector, > } > EXPORT_SYMBOL(drm_connector_attach_max_bpc_property); > > +/** > + * drm_connector_attach_min_bpc_property - attach "min bpc" property > + * @connector: connector to attach min 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_min_bpc_property(struct drm_connector *connector, > + int min, int max) > +{ > + struct drm_device *dev = connector->dev; > + struct drm_property *prop; > + > + prop = connector->min_bpc_property; > + if (!prop) { > + prop = drm_property_create_range(dev, 0, "min bpc", min, max); > + if (!prop) > + return -ENOMEM; > + > + connector->min_bpc_property = prop; > + } > + > + drm_object_attach_property(&connector->base, prop, min); > + connector->state->min_requested_bpc = min; > + connector->state->min_bpc = min; > + > + return 0; > +} > +EXPORT_SYMBOL(drm_connector_attach_min_bpc_property); > + > /** > * drm_connector_attach_hdr_output_metadata_property - attach > "HDR_OUTPUT_METADA" property > * @connector: connector to attach the property on. > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h > index 8f34f4b8183d..7581f965b015 100644 > --- a/include/drm/drm_connector.h > +++ b/include/drm/drm_connector.h > @@ -1126,12 +1126,24 @@ struct drm_connector_state { > */ > u8 max_requested_bpc; > > + /** > + * @min_requested_bpc: Connector property to limit the minimum bit > + * depth of the pixels. > + */ > + u8 min_requested_bpc; > + > /** > * @max_bpc: Connector max_bpc based on the requested max_bpc property > * and the connector bpc limitations obtained from edid. > */ > u8 max_bpc; > > + /** > + * @min_bpc: Connector min_bpc based on the requested min_bpc property > + * and the connector bpc limitations obtained from edid. > + */ > + u8 min_bpc; > + > /** > * @privacy_screen_sw_state: See :ref:`Standard Connector > * Properties<standard_connector_properties>` > @@ -2079,6 +2091,12 @@ struct drm_connector { > */ > struct drm_property *max_bpc_property; > > + /** > + * @min_bpc_property: Default connector property for the min bpc to be > + * driven out of the connector. > + */ > + struct drm_property *min_bpc_property; > + > /** @privacy_screen: drm_privacy_screen for this connector, or NULL. */ > struct drm_privacy_screen *privacy_screen; > > @@ -2482,6 +2500,8 @@ int drm_connector_set_orientation_from_panel( > struct drm_panel *panel); > int drm_connector_attach_max_bpc_property(struct drm_connector *connector, > int min, int max); > +int drm_connector_attach_min_bpc_property(struct drm_connector *connector, > + int min, int max); > void drm_connector_create_privacy_screen_properties(struct drm_connector > *conn); > void drm_connector_attach_privacy_screen_properties(struct drm_connector > *conn); > void drm_connector_attach_privacy_screen_provider( > > base-commit: 098456f3141bf9e0c0d8973695ca38a03465ccd6 > -- > 2.51.1.851.g4ebd6896fd-goog >
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