linux-kernel - [PATCH v2 02/11] drm/bridge: Fix a use case in the bridge disable logic

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Date:   Sun, 26 Nov 2023 16:44:54 +0100
From:   Dario Binacchi <dario.binacchi@...rulasolutions.com>
To:     linux-kernel@...r.kernel.org
Cc:     Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        David Airlie <airlied@...il.com>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH v2 02/11] drm/bridge: Fix a use case in the bridge disable logic

The patch fixes the code for finding the next bridge with the
"pre_enable_prev_first" flag set to false. In case this condition is
not verified, i. e. there is no subsequent bridge with the flag set to
false, the whole bridge list is traversed, invalidating the "next"
variable.

The use of a new iteration variable (i. e. "iter") ensures that the value
of the "next" variable is not invalidated.

Fixes: 4fb912e5e190 ("drm/bridge: Introduce pre_enable_prev_first to alter bridge init order")
Co-developed-by: Michael Trimarchi <michael@...rulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@...rulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
---

(no changes since v1)

 drivers/gpu/drm/drm_bridge.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index f66bf4925dd8..2e5781bf192e 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -662,7 +662,7 @@ void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge,
 					  struct drm_atomic_state *old_state)
 {
 	struct drm_encoder *encoder;
-	struct drm_bridge *next, *limit;
+	struct drm_bridge *iter, *next, *limit;
 
 	if (!bridge)
 		return;
@@ -680,14 +680,15 @@ void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge,
 				 * was enabled first, so disabled last
 				 */
 				limit = next;
+				iter = next;
 
 				/* Find the next bridge that has NOT requested
 				 * prev to be enabled first / disabled last
 				 */
-				list_for_each_entry_from(next, &encoder->bridge_chain,
+				list_for_each_entry_from(iter, &encoder->bridge_chain,
 							 chain_node) {
-					if (!next->pre_enable_prev_first) {
-						next = list_prev_entry(next, chain_node);
+					if (!iter->pre_enable_prev_first) {
+						next = list_prev_entry(iter, chain_node);
 						limit = next;
 						break;
 					}
-- 
2.42.0