linux-kernel - Re: [PATCH 25/29] drm/bridge: Provide pointers to the connector and crtc in bridge state

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Message-ID: <eaardp55onpuqxneh4q6a7tmujglp2pu7kubwisoubjbyuqbt3@zttu7txp34xx>
Date: Thu, 16 Jan 2025 03:04:19 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Douglas Anderson <dianders@...omium.org>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 25/29] drm/bridge: Provide pointers to the connector and
 crtc in bridge state

On Wed, Jan 15, 2025 at 10:05:32PM +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.
> 
> 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@...nel.org>
> ---
>  drivers/gpu/drm/drm_atomic_state_helper.c |  5 +++++
>  drivers/gpu/drm/drm_bridge.c              | 21 +++++++++++++--------
>  include/drm/drm_atomic.h                  | 14 ++++++++++++++
>  3 files changed, 32 insertions(+), 8 deletions(-)
> 
> 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 c937980d6591fd98e33e37d799ebf84e7e6c5529..069c105aa59636c64caffbefcf482133b0db97d9 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -829,19 +829,24 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_enable);
>  
>  static int drm_atomic_bridge_check(struct drm_bridge *bridge,
>  				   struct drm_crtc_state *crtc_state,
>  				   struct drm_connector_state *conn_state)
>  {
> +	struct drm_bridge_state *bridge_state;
> +	int ret;
> +
> +	bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
> +						       bridge);

It felt like an error to me to call this function for a non-atomic
bridges, until I fully followed the code path to find that it will
return NULL if the bridge isn't registered as a private object.

BTW: if my grep-foo isn't deceiving me, we currently have 34 non-atomic
bridges out of 90. Should we start forcebly updating them to use atomic
interface in attempt to drop the mode_fixup() and other non-atomic
callbacks?

> +	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) {
> -		struct drm_bridge_state *bridge_state;
> -		int ret;
> -
> -		bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
> -							       bridge);
> -		if (WARN_ON(!bridge_state))
> -			return -EINVAL;
> -
>  		ret = bridge->funcs->atomic_check(bridge, bridge_state,
>  						  crtc_state, conn_state);
>  		if (ret)
>  			return ret;
>  	} else if (bridge->funcs->mode_fixup) {

-- 
With best wishes
Dmitry