Re: [PATCH v2 1/4] drm/bridge: Add ->detect_ctx hook and drm_bridge_detect_ctx()

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

Hi Luca,

On 1/14/26 12:08 PM, Luca Ceresoli wrote:
> Hello Cristian,
> 
> On Mon Jan 12, 2026 at 11:26 PM CET, Cristian Ciocaltea wrote:
>> Add an atomic variant of the ->detect callback and a new helper to call
>> the hook while passing an optional drm_modeset_acquire_ctx reference.
>>
>> When both ->detect_ctx and ->detect are defined, the latter is ignored.
>> If acquire_ctx is unset, the function takes care of the locking,
>> while also handling EDEADLK.
>>
>> Tested-by: Diederik de Haas <diederik@cknow-tech.com>
>> Tested-by: Maud Spierings <maud_spierings@hotmail.com>
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>> ---
>>  drivers/gpu/drm/drm_bridge.c | 58 ++++++++++++++++++++++++++++++++++++++++++++
>>  include/drm/drm_bridge.h     | 30 +++++++++++++++++++++++
>>  2 files changed, 88 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>> index 6dcf8f6d3ecf..0ef12bf98011 100644
>> --- a/drivers/gpu/drm/drm_bridge.c
>> +++ b/drivers/gpu/drm/drm_bridge.c
>> @@ -1344,6 +1344,64 @@ drm_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector)
>>  }
>>  EXPORT_SYMBOL_GPL(drm_bridge_detect);
>>
>> +/**
>> + * drm_bridge_detect_ctx - check if anything is attached to the bridge output
>> + * @bridge: bridge control structure
>> + * @connector: attached connector
>> + * @ctx: acquire_ctx, or NULL to let this function handle locking
>> + *
>> + * If the bridge supports output detection, as reported by the
>> + * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect_ctx
>> + * or &drm_bridge_funcs.detect for the bridge and return the connection status.
>> + * Otherwise return connector_status_unknown.
>> + *
>> + * When both @ctx and &drm_bridge_funcs.detect_ctx are not set, this helper
>> + * function is equivalent to drm_bridge_detect() above.
>> + *
>> + * RETURNS:
>> + * The detection status on success, or connector_status_unknown if the bridge
>> + * doesn't support output detection.
>> + * If @ctx is set, it might also return -EDEADLK.
>> + */
>> +int drm_bridge_detect_ctx(struct drm_bridge *bridge,
>> +			  struct drm_connector *connector,
>> +			  struct drm_modeset_acquire_ctx *ctx)
> 
> Shouldn't this new function return the same type as detect, i.e. enum
> drm_connector_status?

No, because it might also return an error, as documented in the RETURNS section.
Please also check the comments below.

> 
> Otherwise (see below)...
> 
>> +{
>> +	if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
>> +		return connector_status_unknown;
>> +
>> +	if (bridge->funcs->detect_ctx) {
>> +		struct drm_modeset_acquire_ctx br_ctx;
>> +		int ret;
>> +
>> +		if (ctx)
>> +			return bridge->funcs->detect_ctx(bridge, connector, ctx);
>> +
>> +		drm_modeset_acquire_init(&br_ctx, 0);
>> +retry:
>> +		ret = drm_modeset_lock(&connector->dev->mode_config.connection_mutex,
>> +				       &br_ctx);
>> +		if (!ret)
>> +			ret = bridge->funcs->detect_ctx(bridge, connector, &br_ctx);
>> +
>> +		if (ret == -EDEADLK) {
>> +			drm_modeset_backoff(&br_ctx);
>> +			goto retry;
>> +		}
>> +
>> +		if (ret < 0)
>> +			ret = connector_status_unknown;
>> +
>> +		drm_modeset_drop_locks(&br_ctx);
>> +		drm_modeset_acquire_fini(&br_ctx);
>> +
>> +		return ret;
>> +	}
>> +
>> +	return bridge->funcs->detect(bridge, connector);
> 
> ...here you're converting an enum into an int, which is ok-isk but not
> ideal.

We already have a similar approach with drm_connector_helper_funcs.detect_ctx()
which is expected to return drm_connector_status or the error from
drm_modeset_lock().

> 
>> --- a/include/drm/drm_bridge.h
>> +++ b/include/drm/drm_bridge.h
>> @@ -664,6 +664,33 @@ struct drm_bridge_funcs {
>>  	enum drm_connector_status (*detect)(struct drm_bridge *bridge,
>>  					    struct drm_connector *connector);
>>
>> +	/**
>> +	 * @detect_ctx:
>> +	 *
>> +	 * Check if anything is attached to the bridge output.
>> +	 *
>> +	 * This callback is optional, if not implemented the bridge will be
>> +	 * considered as always having a component attached to its output.
>> +	 * Bridges that implement this callback shall set the
>> +	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
>> +	 *
>> +	 * This is the atomic version of &drm_bridge_funcs.detect.
> 
> I may be missing something, but I'm a bit puzzled by the "atomic" word
> here. For other funcs in this struct there's the old non-atomic func X and
> the new atomic_X func that receives a pointer to struct drm_atomic_state.
> 
> Here I think you are using "atomic" with a more generic meaning. Maybe we'd
> better use another wording to not confuse readers?

This is once again consistent with drm_connector_helper_funcs.detect_ctx()
stating:

  "This is the atomic version of &drm_connector_funcs.detect."

I'm open for changes, but then we should probably do this across all relevant
funcs, beyond current struct scope.

>> +	 *
>> +	 * To avoid races against concurrent connector state updates, the
>> +	 * helper libraries always call this with ctx set to a valid context,
>> +	 * and &drm_mode_config.connection_mutex will always be locked with
>> +	 * the ctx parameter set to this ctx. This allows taking additional
>> +	 * locks as required.
>> +	 *
>> +	 * RETURNS:
>> +	 *
>> +	 * &drm_connector_status indicating the bridge output status,
>> +	 * or the error code returned by drm_modeset_lock(), -EDEADLK.
>> +	 */
>> +	int (*detect_ctx)(struct drm_bridge *bridge,
>> +			  struct drm_connector *connector,
>> +			  struct drm_modeset_acquire_ctx *ctx);
> 
> As above, shouldn't this new func return the same type as detect?

Nope, as explained above.

Thanks,
Cristian