linux-kernel - [PATCH v2 1/3] drm/panel: novatek-nt35560: Fix invalid return value

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Message-ID: <20250729054435.1209156-2-me@brighamcampbell.com>
Date: Mon, 28 Jul 2025 23:44:33 -0600
From: Brigham Campbell <me@...ghamcampbell.com>
To: maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org,
	tzimmermann@...e.de,
	airlied@...il.com,
	simona@...ll.ch,
	linus.walleij@...aro.org,
	neil.armstrong@...aro.org,
	jessica.zhang@....qualcomm.com,
	sam@...nborg.org
Cc: dianders@...omium.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Brigham Campbell <me@...ghamcampbell.com>
Subject: [PATCH v2 1/3] drm/panel: novatek-nt35560: Fix invalid return value

Fix bug in nt35560_set_brightness() which causes the function to
erroneously report an error. mipi_dsi_dcs_write() returns either a
negative value when an error occurred or a positive number of bytes
written when no error occurred. The buggy code reports an error under
either condition.

Fixes: 7835ed6a9e86 ("drm/panel-sony-acx424akp: Modernize backlight handling")
Signed-off-by: Brigham Campbell <me@...ghamcampbell.com>
---
 drivers/gpu/drm/panel/panel-novatek-nt35560.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panel/panel-novatek-nt35560.c b/drivers/gpu/drm/panel/panel-novatek-nt35560.c
index 98f0782c8411..17898a29efe8 100644
--- a/drivers/gpu/drm/panel/panel-novatek-nt35560.c
+++ b/drivers/gpu/drm/panel/panel-novatek-nt35560.c
@@ -161,7 +161,7 @@ static int nt35560_set_brightness(struct backlight_device *bl)
 		par = 0x00;
 		ret = mipi_dsi_dcs_write(dsi, MIPI_DCS_WRITE_CONTROL_DISPLAY,
 					 &par, 1);
-		if (ret) {
+		if (ret < 0) {
 			dev_err(nt->dev, "failed to disable display backlight (%d)\n", ret);
 			return ret;
 		}
-- 
2.50.1