Re: [PATCH v3 31/37] drm/bridge: Provide pointers to the connector and crtc in bridge state

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

On Thu, Feb 13, 2025 at 03:43:50PM +0100, Maxime Ripard wrote:
> Now that connectors are no longer necessarily created by the bridges
> drivers themselves but might be created by drm_bridge_connector, it's
> pretty hard for bridge drivers to retrieve pointers to the connector and
> CRTC they are attached to.
> 
> Indeed, the only way to retrieve the CRTC is to follow the drm_bridge
> encoder field, and then the drm_encoder crtc field, both of them being
> deprecated.

Eh, this isn't quite how this works. So unless bridges have become very
dynamic and gained flexible routing the bridge(->bridge->...)->encoder
chain is static. And the crtc for an encoder you find by walking the
connector states in a drm_atomic_state, finding the right one that points
at your encoder, and then return the ->crtc pointer from that connector
state.

It's a bit bonkers, but I think it's better to compute this than adding
more pointers that potentially diverge. Unless there's a grand plan here,
but then I think we want some safety checks that all the pointers never
get out of sync here.
-Sima

> 
> And for the connector, since we can have multiple connectors attached to
> a CRTC, we don't really have a reliable way to get it.
> 
> Let's provide both pointers in the drm_bridge_state structure so we
> don't have to follow deprecated, non-atomic, pointers, and be more
> consistent with the other KMS entities.
> 
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> ---
>  drivers/gpu/drm/drm_atomic_state_helper.c |  5 +++++
>  drivers/gpu/drm/drm_bridge.c              |  5 +++++
>  include/drm/drm_atomic.h                  | 14 ++++++++++++++
>  3 files changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index 519228eb109533d2596e899a57b571fa0995824f..66661dca077215b78dffca7bc1712f56d35e3918 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -777,10 +777,15 @@ EXPORT_SYMBOL(drm_atomic_helper_bridge_duplicate_state);
>   * that don't subclass the bridge state.
>   */
>  void drm_atomic_helper_bridge_destroy_state(struct drm_bridge *bridge,
>  					    struct drm_bridge_state *state)
>  {
> +	if (state->connector) {
> +		drm_connector_put(state->connector);
> +		state->connector = NULL;
> +	}
> +
>  	kfree(state);
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_bridge_destroy_state);
>  
>  /**
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index b6d24092674c8fa33d9b6ebab9ece0f91fb8f8ea..db2e9834939217d65720ab7a2f82a9ca3db796b0 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -812,10 +812,15 @@ static int drm_atomic_bridge_check(struct drm_bridge *bridge,
>  		bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
>  							       bridge);
>  		if (WARN_ON(!bridge_state))
>  			return -EINVAL;
>  
> +		bridge_state->crtc = crtc_state->crtc;
> +
> +		drm_connector_get(conn_state->connector);
> +		bridge_state->connector = conn_state->connector;
> +
>  		if (bridge->funcs->atomic_check) {
>  			ret = bridge->funcs->atomic_check(bridge, bridge_state,
>  							  crtc_state, conn_state);
>  			if (ret)
>  				return ret;
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 4c673f0698fef6b60f77db980378d5e88e0e250e..293e2538a428bc14013d7fabea57a6b858ed7b47 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -1216,10 +1216,24 @@ struct drm_bridge_state {
>  	/**
>  	 * @bridge: the bridge this state refers to
>  	 */
>  	struct drm_bridge *bridge;
>  
> +	/**
> +	 * @crtc: CRTC the bridge is connected to, NULL if disabled.
> +	 *
> +	 * Do not change this directly.
> +	 */
> +	struct drm_crtc *crtc;
> +
> +	/**
> +	 * @connector: The connector the bridge is connected to, NULL if disabled.
> +	 *
> +	 * Do not change this directly.
> +	 */
> +	struct drm_connector *connector;
> +
>  	/**
>  	 * @input_bus_cfg: input bus configuration
>  	 */
>  	struct drm_bus_cfg input_bus_cfg;
>  
> 
> -- 
> 2.48.0
> 

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