From 3b28281317e57cc729b23caa3a59882f1eb40e92 Mon Sep 17 00:00:00 2001 From: Mattias Jacobsson <2pi@mok.nu> Date: Mon, 2 Dec 2019 21:06:22 +0800 Subject: [PATCH] USB: misc: appledisplay: fix backlight update_status return code [ Upstream commit 090158555ff8d194a98616034100b16697dd80d0 ] 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 Signed-off-by: Sasha Levin Signed-off-by: Yang Yingliang --- 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 1c6da8d6cccf..39ca31b4de46 100644 --- a/drivers/usb/misc/appledisplay.c +++ b/drivers/usb/misc/appledisplay.c @@ -148,8 +148,11 @@ 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) -- GitLab