linux-kernel - Re: [PATCH 05/29] drm/atomic_state_helper: Fix bridge state initialization

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Message-ID: <9f17dfd9-a4d4-41e9-b988-bd8ca858e5e7@suse.de>
Date: Tue, 2 Sep 2025 15:18:17 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Maxime Ripard <mripard@...nel.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 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>,
 Jyri Sarha <jyri.sarha@....fi>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Devarsh Thakkar <devarsht@...com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/29] drm/atomic_state_helper: Fix bridge state
 initialization

Hi

Am 02.09.25 um 10:32 schrieb Maxime Ripard:
> Bridges implement their state using a drm_private_obj and an
> hand-crafted reset implementation.
>
> Since drm_private_obj doesn't have a set of reset helper like the other
> states, __drm_atomic_helper_bridge_reset() was initializing both the
> drm_private_state and the drm_bridge_state structures.
>
> This initialization however was missing the drm_private_state.obj
> pointer to the drm_private_obj the state was allocated for, creating a
> NULL pointer dereference when trying to access it.
>
> Fixes: 751465913f04 ("drm/bridge: Add a drm_bridge_state object")
> Signed-off-by: Maxime Ripard <mripard@...nel.org>
> ---
>   drivers/gpu/drm/drm_atomic_state_helper.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index 7142e163e618ea0d7d9d828e1bd9ff2a6ec0dfeb..b962c342b16aabf4e3bea52a914e5deb1c2080ce 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -707,10 +707,17 @@ void drm_atomic_helper_connector_destroy_state(struct drm_connector *connector,
>   	__drm_atomic_helper_connector_destroy_state(state);
>   	kfree(state);
>   }
>   EXPORT_SYMBOL(drm_atomic_helper_connector_destroy_state);
>   
> +static void __drm_atomic_helper_private_obj_reset(struct drm_private_obj *obj,
> +						  struct drm_private_state *state)
> +{
> +	memset(state, 0, sizeof(*state));

This argument is guaranteed to be zero'd, I think. No need for a memset.

> +	state->obj = obj;
> +}
> +
>   /**
>    * __drm_atomic_helper_private_obj_duplicate_state - copy atomic private state
>    * @obj: CRTC object
>    * @state: new private object state
>    *
> @@ -796,10 +803,11 @@ EXPORT_SYMBOL(drm_atomic_helper_bridge_destroy_state);
>    */
>   void __drm_atomic_helper_bridge_reset(struct drm_bridge *bridge,
>   				      struct drm_bridge_state *state)
>   {
>   	memset(state, 0, sizeof(*state));

Another unnecessary memset?

Best regards
Thomas

> +	__drm_atomic_helper_private_obj_reset(&bridge->base, &state->base);
>   	state->bridge = bridge;
>   }
>   EXPORT_SYMBOL(__drm_atomic_helper_bridge_reset);
>   
>   /**
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)