FAILED: patch "[PATCH] tilcdc: tilcdc_external: fix an incorrect NULL check on list" failed to apply to 4.19-stable tree

FAILED: patch "[PATCH] tilcdc: tilcdc_external: fix an incorrect NULL check on list" failed to apply to 4.19-stable tree

[gregkh]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8b917cbe38e9b0d002492477a9fc2bfee2412ce4 Mon Sep 17 00:00:00 2001
From: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Date: Sun, 27 Mar 2022 14:15:16 +0800
Subject: [PATCH] tilcdc: tilcdc_external: fix an incorrect NULL check on list
 iterator

The bug is here:
	if (!encoder) {

The list iterator value 'encoder' will *always* be set and non-NULL
by list_for_each_entry(), so it is incorrect to assume that the
iterator value will be NULL if the list is empty or no element
is found.

To fix the bug, use a new variable 'iter' as the list iterator,
while use the original variable 'encoder' as a dedicated pointer
to point to the found element.

Cc: stable@vger.kernel.org
Fixes: ec9eab097a500 ("drm/tilcdc: Add drm bridge support for attaching drm bridge drivers")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>
Tested-by: Jyri Sarha <jyri.sarha@iki.fi>
Signed-off-by: Jyri Sarha <jyri.sarha@iki.fi>
Link: https://patchwork.freedesktop.org/patch/msgid/20220327061516.5076-1-xiam0nd.tong@gmail.com

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_external.c b/drivers/gpu/drm/tilcdc/tilcdc_external.c
index 7594cf6e186e..3b86d002ef62 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_external.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_external.c
@@ -60,11 +60,13 @@ struct drm_connector *tilcdc_encoder_find_connector(struct drm_device *ddev,
 int tilcdc_add_component_encoder(struct drm_device *ddev)
 {
 	struct tilcdc_drm_private *priv = ddev->dev_private;
-	struct drm_encoder *encoder;
+	struct drm_encoder *encoder = NULL, *iter;
 
-	list_for_each_entry(encoder, &ddev->mode_config.encoder_list, head)
-		if (encoder->possible_crtcs & (1 << priv->crtc->index))
+	list_for_each_entry(iter, &ddev->mode_config.encoder_list, head)
+		if (iter->possible_crtcs & (1 << priv->crtc->index)) {
+			encoder = iter;
 			break;
+		}
 
 	if (!encoder) {
 		dev_err(ddev->dev, "%s: No suitable encoder found\n", __func__);