Re: [PATCH v2 01/20] drm/atomic: Handle max bpc properties before connector state allocation

[Chaoyi Chen]

Hi Xilin,

On 10/9/2026 11:15 AM, Xilin Wu wrote:
> Allow drivers to attach the max bpc property before allocating connector
> state, as needed by the upcoming non-HDMI bridge connector support.
> Only update the current state when one exists.
> 
> Initialize max_requested_bpc and max_bpc from the attached property default
> when creating connector state. Use drm_object_property_get_default_value()
> rather than the range maximum so that state creation and subsequent resets
> restore the value chosen when attaching the property.
> 
> Cover deferred allocation, existing state and restoration of a default
> that differs from the range maximum in the connector KUnit tests.
> 
> Assisted-by: LLM
> Signed-off-by: Xilin Wu <sophon@xxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_atomic_state_helper.c  |  8 +++++
>  drivers/gpu/drm/drm_connector.c            |  6 ++--
>  drivers/gpu/drm/tests/drm_connector_test.c | 53 ++++++++++++++++++++++++++++++
>  3 files changed, 65 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index a2ef272e9f27..8352b5a9097a 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -494,7 +494,15 @@ void
>  __drm_atomic_helper_connector_state_init(struct drm_connector_state *conn_state,
>  					 struct drm_connector *connector)
>  {
> +	u64 val;
> +
>  	conn_state->connector = connector;
> +	if (connector->max_bpc_property &&
> +	    !drm_object_property_get_default_value(&connector->base,
> +						   connector->max_bpc_property, &val)) {
> +		conn_state->max_requested_bpc = val;
> +		conn_state->max_bpc = val;
> +	}
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_state_init);
>  
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 8b4baed060f3..34c30469f405 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -2886,8 +2886,10 @@ int drm_connector_attach_max_bpc_property(struct drm_connector *connector,
>  	}
>  
>  	drm_object_attach_property(&connector->base, prop, max);
> -	connector->state->max_requested_bpc = max;
> -	connector->state->max_bpc = max;
> +	if (connector->state) {
> +		connector->state->max_requested_bpc = max;
> +		connector->state->max_bpc = max;
> +	}
> 

And for patch1/2. I don't think it's right way to go.

As comment said: 
drm_connector_attach_max_bpc_property() requires the connector to have a state.

There are two reasons here. First, most drivers follow the convention
described in this comment, but you only modified some of them. Second, 
it appears you are removing the connector state, so the 
"if (connector->state)" check here would always evaluate to false, 
which doesn't seem to make much sense.

>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/tests/drm_connector_test.c b/drivers/gpu/drm/tests/drm_connector_test.c
> index beb1d50a6646..1174607441b9 100644
> --- a/drivers/gpu/drm/tests/drm_connector_test.c
> +++ b/drivers/gpu/drm/tests/drm_connector_test.c
> @@ -12,6 +12,7 @@
>  #include <drm/drm_file.h>
>  #include <drm/drm_kunit_helpers.h>
>  #include <drm/drm_modes.h>
> +#include <drm/drm_property.h>
>  
>  #include <drm/display/drm_hdmi_helper.h>
>  
> @@ -187,7 +188,59 @@ KUNIT_ARRAY_PARAM(drm_connector_init_type_valid,
>  		  drm_connector_init_type_valid_tests,
>  		  drm_connector_init_type_desc);
>  
> +/* The attached default need not equal the upper end of the property range. */
> +static void drm_test_connector_max_bpc_default(struct kunit *test)
> +{
> +	struct drm_connector_init_priv *priv = test->priv;
> +	struct drm_connector *connector = &priv->connector;
> +	struct drm_property *prop;
> +	int ret;
> +
> +	ret = drmm_connector_init(&priv->drm, connector, &dummy_funcs,
> +				  DRM_MODE_CONNECTOR_DisplayPort, NULL);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +
> +	prop = drm_property_create_range(&priv->drm, 0, "max bpc", 6, 12);
> +	KUNIT_ASSERT_NOT_NULL(test, prop);
> +	connector->max_bpc_property = prop;
> +	ret = drm_connector_attach_max_bpc_property(connector, 6, 10);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +	KUNIT_EXPECT_NULL(test, connector->state);
> +
> +	drm_mode_config_reset(&priv->drm);
> +	KUNIT_ASSERT_NOT_NULL(test, connector->state);
> +	KUNIT_EXPECT_EQ(test, connector->state->max_requested_bpc, 10);
> +	KUNIT_EXPECT_EQ(test, connector->state->max_bpc, 10);
> +
> +	connector->state->max_requested_bpc = 8;
> +	connector->state->max_bpc = 8;
> +	drm_mode_config_reset(&priv->drm);
> +	KUNIT_ASSERT_NOT_NULL(test, connector->state);
> +	KUNIT_EXPECT_EQ(test, connector->state->max_requested_bpc, 10);
> +	KUNIT_EXPECT_EQ(test, connector->state->max_bpc, 10);
> +}
> +
> +static void drm_test_connector_max_bpc_existing_state(struct kunit *test)
> +{
> +	struct drm_connector_init_priv *priv = test->priv;
> +	struct drm_connector *connector = &priv->connector;
> +	int ret;
> +
> +	ret = drmm_connector_init(&priv->drm, connector, &dummy_funcs,
> +				  DRM_MODE_CONNECTOR_DisplayPort, NULL);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +	drm_mode_config_reset(&priv->drm);
> +	KUNIT_ASSERT_NOT_NULL(test, connector->state);
> +
> +	ret = drm_connector_attach_max_bpc_property(connector, 6, 10);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +	KUNIT_EXPECT_EQ(test, connector->state->max_requested_bpc, 10);
> +	KUNIT_EXPECT_EQ(test, connector->state->max_bpc, 10);
> +}
> +
>  static struct kunit_case drmm_connector_init_tests[] = {
> +	KUNIT_CASE(drm_test_connector_max_bpc_default),
> +	KUNIT_CASE(drm_test_connector_max_bpc_existing_state),
>  	KUNIT_CASE(drm_test_drmm_connector_init),
>  	KUNIT_CASE(drm_test_drmm_connector_init_null_ddc),
>  	KUNIT_CASE_PARAM(drm_test_drmm_connector_init_type_valid,
> 

-- 
Best, 
Chaoyi