linux-kernel - Re: [PATCH v1 1/2] pwm: bcm-iproc: handle clk_get

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Date:   Mon, 23 Mar 2020 09:25:40 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Yendapally Reddy Dhananjaya Reddy 
        <yendapally.reddy@...adcom.com>, linux-pwm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] pwm: bcm-iproc: handle clk_get_rate() return

On Mon, Mar 23, 2020 at 12:23:17PM +0530, Rayagonda Kokatanur wrote:
> Handle clk_get_rate() returning <= 0 condition to avoid
> possible division by zero.

Was this noticed during a review and is more theoretic. Or does this
(depending on pre-boot state) result in a kernel crash?

> Fixes: daa5abc41c80 ("pwm: Add support for Broadcom iProc PWM controller")
> Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
> ---
>  drivers/pwm/pwm-bcm-iproc.c | 32 +++++++++++++++++++-------------
>  1 file changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-bcm-iproc.c b/drivers/pwm/pwm-bcm-iproc.c
> index 1f829edd8ee7..8bbd2a04fead 100644
> --- a/drivers/pwm/pwm-bcm-iproc.c
> +++ b/drivers/pwm/pwm-bcm-iproc.c
> @@ -99,19 +99,25 @@ static void iproc_pwmc_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
>  	else
>  		state->polarity = PWM_POLARITY_INVERSED;
>  
> -	value = readl(ip->base + IPROC_PWM_PRESCALE_OFFSET);
> -	prescale = value >> IPROC_PWM_PRESCALE_SHIFT(pwm->hwpwm);
> -	prescale &= IPROC_PWM_PRESCALE_MAX;
> -
> -	multi = NSEC_PER_SEC * (prescale + 1);
> -
> -	value = readl(ip->base + IPROC_PWM_PERIOD_OFFSET(pwm->hwpwm));
> -	tmp = (value & IPROC_PWM_PERIOD_MAX) * multi;
> -	state->period = div64_u64(tmp, rate);
> -
> -	value = readl(ip->base + IPROC_PWM_DUTY_CYCLE_OFFSET(pwm->hwpwm));
> -	tmp = (value & IPROC_PWM_PERIOD_MAX) * multi;
> -	state->duty_cycle = div64_u64(tmp, rate);
> +	if (rate == 0) {
> +		state->period = 0;
> +		state->duty_cycle = 0;
> +	} else {
> +		value = readl(ip->base + IPROC_PWM_PRESCALE_OFFSET);
> +		prescale = value >> IPROC_PWM_PRESCALE_SHIFT(pwm->hwpwm);
> +		prescale &= IPROC_PWM_PRESCALE_MAX;
> +
> +		multi = NSEC_PER_SEC * (prescale + 1);
> +
> +		value = readl(ip->base + IPROC_PWM_PERIOD_OFFSET(pwm->hwpwm));
> +		tmp = (value & IPROC_PWM_PERIOD_MAX) * multi;
> +		state->period = div64_u64(tmp, rate);
> +
> +		value = readl(ip->base +
> +			      IPROC_PWM_DUTY_CYCLE_OFFSET(pwm->hwpwm));
> +		tmp = (value & IPROC_PWM_PERIOD_MAX) * multi;
> +		state->duty_cycle = div64_u64(tmp, rate);
> +	}

The change looks fine.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |