linux-kernel - Re: [PATCH v2 29/35] drm/bridge: Assume that a bridge is atomic if it has atomic

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Message-ID: <stisurekwcm2jmh7qb5rm3nvh4us2oy2c26mhdvqf2nivoa4en@xs5m6rygbxkp>
Date: Sun, 9 Feb 2025 08:18:10 +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 v2 29/35] drm/bridge: Assume that a bridge is atomic if
 it has atomic_reset

On Tue, Feb 04, 2025 at 03:57:57PM +0100, Maxime Ripard wrote:
> A bridge is considered atomic-enabled if it has an atomic_check

I think this part of the explanation is a bit misleading. This code just
checks if there is a need to atomic_check() it.

> implementation. However, atomic_check is optional and thus a driver
> might very well not provide an implementation, and yet still be atomic.

I think the change is correct, but I'd rather suggest implementing
separate drm_bridge_has_atomic_state() helper and using it here and in
two other cases.

> 
> Switch to atomic_reset, which allocates the initial bridge state and is
> thus a better candidate.
> 
> Signed-off-by: Maxime Ripard <mripard@...nel.org>
> ---
>  drivers/gpu/drm/drm_bridge.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index d7c17a26e86fd9a3e5a39f335edff4ffce30dd79..ad91a0ac375a9c8cf82834354ec7f654a59a7292 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -794,23 +794,25 @@ 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)
>  {
> -	if (bridge->funcs->atomic_check) {
> +	if (bridge->funcs->atomic_reset) {
>  		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;
> +		if (bridge->funcs->atomic_check) {
> +			ret = bridge->funcs->atomic_check(bridge, bridge_state,
> +							  crtc_state, conn_state);
> +			if (ret)
> +				return ret;
> +		}
>  	} else if (bridge->funcs->mode_fixup) {
>  		if (!bridge->funcs->mode_fixup(bridge, &crtc_state->mode,
>  					       &crtc_state->adjusted_mode))
>  			return -EINVAL;
>  	}
> 
> -- 
> 2.48.0
> 

-- 
With best wishes
Dmitry