Re: [PATCH v5 04/16] drm/atomic: Introduce helper to lookup connector by encoder

[Simona Vetter <simona.vetter@ffwll.ch>]

On Tue, Mar 04, 2025 at 12:10:47PM +0100, Maxime Ripard wrote:
> With the bridges switching over to drm_bridge_connector, the direct
> association between a bridge driver and its connector was lost.
> 
> This is mitigated for atomic bridge drivers by the fact you can access
> the encoder, and then call drm_atomic_get_old_connector_for_encoder() or
> drm_atomic_get_new_connector_for_encoder() with drm_atomic_state.
> 
> This was also made easier by providing drm_atomic_state directly to all
> atomic hooks bridges can implement.
> 
> However, bridge drivers don't have a way to access drm_atomic_state
> outside of the modeset path, like from the hotplug interrupt path or any
> interrupt handler.
> 
> Let's introduce a function to retrieve the connector currently assigned
> to an encoder, without using drm_atomic_state, to make these drivers'
> life easier.
> 
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> Co-developed-by: Simona Vetter <simona.vetter@ffwll.ch>
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> ---
>  drivers/gpu/drm/drm_atomic.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_atomic.h     |  3 +++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 9ea2611770f43ce7ccba410406d5f2c528aab022..b926b132590e78f8d41d48eb4da4bccf170ee236 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -985,10 +985,55 @@ drm_atomic_get_new_connector_for_encoder(const struct drm_atomic_state *state,
>  
>  	return NULL;
>  }
>  EXPORT_SYMBOL(drm_atomic_get_new_connector_for_encoder);
>  
> +/**
> + * drm_atomic_get_connector_for_encoder - Get connector currently assigned to an encoder
> + * @encoder: The encoder to find the connector of
> + * @ctx: Modeset locking context
> + *
> + * This function finds and returns the connector currently assigned to
> + * an @encoder.

I think it'd be good to link to the other atomic connector functions like
drm_atomic_get_old/new_connector_for_encoder and explain when to use them.
So also add links to the kerneldoc of these other functions pointing to
here.

- This function is for detect, link repair or anything else that comes
  from the hardware. Or in general, anything that's not in atomic
  commit/check code paths.

- In atomic check/commit code you want to use the other functions.

Otherwise people will have an even harder time finding the right variant
in this maze of look-alikes :-)

With the kerneldoc suitably polished:

Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Simona Vetter <simona.vetter@intel.com>

> + *
> + * Returns:
> + * The connector connected to @encoder, or an error pointer otherwise.
> + * When the error is EDEADLK, a deadlock has been detected and the
> + * sequence must be restarted.
> + */
> +struct drm_connector *
> +drm_atomic_get_connector_for_encoder(const struct drm_encoder *encoder,
> +				     struct drm_modeset_acquire_ctx *ctx)
> +{
> +	struct drm_connector_list_iter conn_iter;
> +	struct drm_connector *out_connector = ERR_PTR(-EINVAL);
> +	struct drm_connector *connector;
> +	struct drm_device *dev = encoder->dev;
> +	int ret;
> +
> +	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	drm_connector_list_iter_begin(dev, &conn_iter);
> +	drm_for_each_connector_iter(connector, &conn_iter) {
> +		if (!connector->state)
> +			continue;
> +
> +		if (encoder == connector->state->best_encoder) {
> +			out_connector = connector;
> +			break;
> +		}
> +	}
> +	drm_connector_list_iter_end(&conn_iter);
> +	drm_modeset_unlock(&dev->mode_config.connection_mutex);
> +
> +	return out_connector;
> +}
> +EXPORT_SYMBOL(drm_atomic_get_connector_for_encoder);
> +
> +
>  /**
>   * drm_atomic_get_old_crtc_for_encoder - Get old crtc for an encoder
>   * @state: Atomic state
>   * @encoder: The encoder to fetch the crtc state for
>   *
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 4c673f0698fef6b60f77db980378d5e88e0e250e..38636a593c9d98cadda85ccd67326cb152f0dd27 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -623,10 +623,13 @@ struct drm_connector *
>  drm_atomic_get_old_connector_for_encoder(const struct drm_atomic_state *state,
>  					 struct drm_encoder *encoder);
>  struct drm_connector *
>  drm_atomic_get_new_connector_for_encoder(const struct drm_atomic_state *state,
>  					 struct drm_encoder *encoder);
> +struct drm_connector *
> +drm_atomic_get_connector_for_encoder(const struct drm_encoder *encoder,
> +				     struct drm_modeset_acquire_ctx *ctx);
>  
>  struct drm_crtc *
>  drm_atomic_get_old_crtc_for_encoder(struct drm_atomic_state *state,
>  					 struct drm_encoder *encoder);
>  struct drm_crtc *
> 
> -- 
> 2.48.1
> 

-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch