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From:   =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= <linux@weissschuh.net>
To:     Lee Jones <lee.jones@linaro.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org
Cc:     =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= <linux@weissschuh.net>,
        linux-kernel@vger.kernel.org
Subject: [PATCH] backlight: propagate errors from get_brightness()
Date:   Mon,  6 Sep 2021 23:55:25 +0200
Message-Id: <20210906215525.15418-1-linux@weissschuh.net>
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Precedence: bulk

backlight.h documents "struct backlight_ops->get_brightness()" to return
a negative errno on failure.
So far these errors have not been handled in the backlight core.
This leads to negative values being exposed through sysfs although only
positive values are documented to be reported.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 drivers/video/backlight/backlight.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 537fe1b376ad..d681962f8509 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -292,10 +292,13 @@ static ssize_t actual_brightness_show(struct device *dev,
 	struct backlight_device *bd = to_backlight_device(dev);
 
 	mutex_lock(&bd->ops_lock);
-	if (bd->ops && bd->ops->get_brightness)
-		rc = sprintf(buf, "%d\n", bd->ops->get_brightness(bd));
-	else
+	if (bd->ops && bd->ops->get_brightness) {
+		rc = bd->ops->get_brightness(bd);
+		if (rc >= 0)
+			rc = sprintf(buf, "%d\n", rc);
+	} else {
 		rc = sprintf(buf, "%d\n", bd->props.brightness);
+	}
 	mutex_unlock(&bd->ops_lock);
 
 	return rc;
@@ -381,9 +384,18 @@ ATTRIBUTE_GROUPS(bl_device);
 void backlight_force_update(struct backlight_device *bd,
 			    enum backlight_update_reason reason)
 {
+	int brightness;
+
 	mutex_lock(&bd->ops_lock);
-	if (bd->ops && bd->ops->get_brightness)
-		bd->props.brightness = bd->ops->get_brightness(bd);
+	if (bd->ops && bd->ops->get_brightness) {
+		brightness = bd->ops->get_brightness(bd);
+		if (brightness >= 0)
+			bd->props.brightness = brightness;
+		else
+			dev_warn(&bd->dev,
+				 "Could not update brightness from device: errno = %d",
+				 -brightness);
+	}
 	mutex_unlock(&bd->ops_lock);
 	backlight_generate_event(bd, reason);
 }

base-commit: 79fad92f2e596f5a8dd085788a24f540263ef887
-- 
2.33.0