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USB: misc: appledisplay: fix backlight update_status return code 

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>
This commit is contained in:
Mattias Jacobsson 2018-10-16 14:20:08 +02:00 committed by Greg Kroah-Hartman
parent 644930cbad
commit 090158555f
1 changed files with 5 additions and 2 deletions
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7
drivers/usb/misc/appledisplay.c
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@ -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)