linux-kernel - Re: [PATCH] leds: leds-pwm: fix duty time overflow.

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Message-ID: <CAK5ve-JQEX5yOCW7vxu1yq7RrCUH0aWSrEJ0eBqSoOtMnjHEVg@mail.gmail.com>
Date:	Wed, 11 Dec 2013 11:07:53 -0800
From:	Bryan Wu <cooloney@...il.com>
To:	Xiubo Li <Li.Xiubo@...escale.com>
Cc:	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	Linux LED Subsystem <linux-leds@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>, b47053@...escale.com
Subject: Re: [PATCH] leds: leds-pwm: fix duty time overflow.

On Wed, Dec 11, 2013 at 1:19 AM, Xiubo Li <Li.Xiubo@...escale.com> wrote:
> Overflow maybe occurs when calculates the duty time. For instance,
> the period time is 990000000ns, and the max_brightness is 127, when
> setting the brightness to 12, the duty value will be 25906026ns, but
> it should be 93543307ns.

This looks good to me. Good catch. I will merge this.

Thanks,
-Bryan


> ---
>  drivers/leds/leds-pwm.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
> index bb6f948..7cb2cd8 100644
> --- a/drivers/leds/leds-pwm.c
> +++ b/drivers/leds/leds-pwm.c
> @@ -66,9 +66,11 @@ static void led_pwm_set(struct led_classdev *led_cdev,
>         struct led_pwm_data *led_dat =
>                 container_of(led_cdev, struct led_pwm_data, cdev);
>         unsigned int max = led_dat->cdev.max_brightness;
> -       unsigned int period =  led_dat->period;
> +       unsigned long long duty =  led_dat->period;
>
> -       led_dat->duty = brightness * period / max;
> +       duty *= brightness;
> +       do_div(duty, max);
> +       led_dat->duty = duty;
>
>         if (led_dat->can_sleep)
>                 schedule_work(&led_dat->work);
> --
> 1.8.4
>
>
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