linux-kernel - Re: [PATCH] pwm: bcm-iproc: handle clk_get

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Message-ID: <94f2aed1-d88d-3ee0-6e57-917f665951f2@broadcom.com>
Date:   Fri, 17 Jul 2020 10:22:13 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Scott Branden <scott.branden@...adcom.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>
Cc:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
Subject: Re: [PATCH] pwm: bcm-iproc: handle clk_get_rate() return



On 7/17/2020 10:07 AM, Scott Branden wrote:
> From: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
> 
> Handle clk_get_rate() returning <= 0 condition to avoid
> possible division by zero.
> 
> Fixes: daa5abc41c80 ("pwm: Add support for Broadcom iProc PWM controller")
> Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
> Signed-off-by: Scott Branden <scott.branden@...adcom.com>
> ---
>  drivers/pwm/pwm-bcm-iproc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pwm/pwm-bcm-iproc.c b/drivers/pwm/pwm-bcm-iproc.c
> index 1f829edd8ee7..72a8607b6c8d 100644
> --- a/drivers/pwm/pwm-bcm-iproc.c
> +++ b/drivers/pwm/pwm-bcm-iproc.c
> @@ -86,6 +86,11 @@ static void iproc_pwmc_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
>  	u32 value, prescale;
>  
>  	rate = clk_get_rate(ip->clk);
> +	if (rate == 0) {
> +		state->period = 0;
> +		state->duty_cycle = 0;
> +		return;
> +	}

Based on the pwm core code, 'get_state' expects the following fields to
be populated: 'polarity', 'enabled', 'period', and 'duty cycle'.

The above logic will leave 'polarity' and 'enabled' completely
unpopulated when clock rate is zero.

>  
>  	value = readl(ip->base + IPROC_PWM_CTRL_OFFSET);
>  
>