linux-kernel - [PATCH v2] drm/edid: Fix uninitialized variable in drm_cvt

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Message-Id: <20201103221510.575827-1-lyude@redhat.com>
Date:   Tue,  3 Nov 2020 17:15:10 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Ilia Mirkin <imirkin@...m.mit.edu>, stable@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Kees Cook <keescook@...omium.org>,
        Leon Romanovsky <leon@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Chao Yu <chao@...nel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2] drm/edid: Fix uninitialized variable in drm_cvt_modes()

Noticed this when trying to compile with -Wall on a kernel fork. We potentially
don't set width here, which causes the compiler to complain about width
potentially being uninitialized in drm_cvt_modes(). So, let's fix that.

Changes since v1:
* Don't emit an error as this code isn't reachable, just mark it as such

Signed-off-by: Lyude Paul <lyude@...hat.com>

Cc: <stable@...r.kernel.org> # v5.9+
Fixes: 3f649ab728cd ("treewide: Remove uninitialized_var() usage")
Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 drivers/gpu/drm/drm_edid.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 631125b46e04..0643b98c6383 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -3094,6 +3094,7 @@ static int drm_cvt_modes(struct drm_connector *connector,
 
 	for (i = 0; i < 4; i++) {
 		int width, height;
+		u8 cvt_aspect_ratio;
 
 		cvt = &(timing->data.other_data.data.cvt[i]);
 
@@ -3101,7 +3102,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
 			continue;
 
 		height = (cvt->code[0] + ((cvt->code[1] & 0xf0) << 4) + 1) * 2;
-		switch (cvt->code[1] & 0x0c) {
+		cvt_aspect_ratio = cvt->code[1] & 0x0c;
+		switch (cvt_aspect_ratio) {
 		case 0x00:
 			width = height * 4 / 3;
 			break;
@@ -3114,6 +3116,8 @@ static int drm_cvt_modes(struct drm_connector *connector,
 		case 0x0c:
 			width = height * 15 / 9;
 			break;
+		default:
+			unreachable();
 		}
 
 		for (j = 1; j < 5; j++) {
-- 
2.28.0