This is a note to let you know that I've just added the patch titled
backlight: pwm_bl: Fix overflow condition
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: backlight-pwm_bl-fix-overflow-condition.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Dec 21 09:02:40 CET 2017
From: Derek Basehore dbasehore@chromium.org Date: Tue, 29 Aug 2017 13:34:34 -0700 Subject: backlight: pwm_bl: Fix overflow condition
From: Derek Basehore dbasehore@chromium.org
[ Upstream commit 5d0c49acebc9488e37db95f1d4a55644e545ffe7 ]
This fixes an overflow condition that can happen with high max brightness and period values in compute_duty_cycle. This fixes it by using a 64 bit variable for computing the duty cycle.
Signed-off-by: Derek Basehore dbasehore@chromium.org Acked-by: Thierry Reding thierry.reding@gmail.com Reviewed-by: Brian Norris briannorris@chromium.org Signed-off-by: Lee Jones lee.jones@linaro.org Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/video/backlight/pwm_bl.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -79,14 +79,17 @@ static void pwm_backlight_power_off(stru static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness) { unsigned int lth = pb->lth_brightness; - int duty_cycle; + u64 duty_cycle;
if (pb->levels) duty_cycle = pb->levels[brightness]; else duty_cycle = brightness;
- return (duty_cycle * (pb->period - lth) / pb->scale) + lth; + duty_cycle *= pb->period - lth; + do_div(duty_cycle, pb->scale); + + return duty_cycle + lth; }
static int pwm_backlight_update_status(struct backlight_device *bl)
Patches currently in stable-queue which might be from dbasehore@chromium.org are
queue-4.9/backlight-pwm_bl-fix-overflow-condition.patch