From 090158555ff8d194a98616034100b16697dd80d0 Mon Sep 17 00:00:00 2001
From: Mattias Jacobsson <2pi@mok.nu>
Date: Tue, 16 Oct 2018 14:20:08 +0200
Subject: [PATCH] USB: misc: appledisplay: fix backlight update_status return code
Git-commit: 090158555ff8d194a98616034100b16697dd80d0
Patch-mainline: v4.20-rc1
References: bsc#1051510
Upon success the update_status handler returns a positive number
corresponding to the number of bytes transferred by usb_control_msg.
However the return code of the update_status handler should indicate if
an error occurred(negative) or how many bytes of the user's input to sysfs
that was consumed. Return code zero indicates all bytes were consumed.
The bug can for example result in the update_status handler being called
twice, the second time with only the "unconsumed" part of the user's input
to sysfs. Effectively setting an incorrect brightness.
Change the update_status handler to return zero for all successful
transactions and forward usb_control_msg's error code upon failure.
Signed-off-by: Mattias Jacobsson <2pi@mok.nu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/usb/misc/appledisplay.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c
index d746c26a8055..bd539f3058bc 100644
--- a/drivers/usb/misc/appledisplay.c
+++ b/drivers/usb/misc/appledisplay.c
@@ -146,8 +146,11 @@ static int appledisplay_bl_update_status(struct backlight_device *bd)
pdata->msgdata, 2,
ACD_USB_TIMEOUT);
mutex_unlock(&pdata->sysfslock);
-
- return retval;
+
+ if (retval < 0)
+ return retval;
+ else
+ return 0;
}
static int appledisplay_bl_get_brightness(struct backlight_device *bd)
--
2.16.4