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

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Date:   Mon, 23 Mar 2020 14:35:27 +0530
From:   Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        BCM Kernel Feedback <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 Mailing List <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 1:55 PM Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> 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?

This is reported by internal coverity tool.
>
> > 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/ |