linux-kernel - Re: [PATCH v12 10/11] clk: pwm: Use 64-bit division function

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Date:   Fri, 10 Apr 2020 12:15:03 -0700
From:   Guru Das Srinagesh <gurus@...eaurora.org>
To:     linux-pwm@...r.kernel.org
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Subbaraman Narayanamurthy <subbaram@...eaurora.org>,
        David Collins <collinsd@...eaurora.org>,
        linux-kernel@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
        David Laight <David.Laight@...LAB.COM>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v12 10/11] clk: pwm: Use 64-bit division function

+ Arnd, David

On Wed, Apr 08, 2020 at 11:52:39PM -0700, Guru Das Srinagesh wrote:
> Since the PWM framework is switching struct pwm_args.period's datatype
> to u64, prepare for this transition by using div64_u64 to handle a
> 64-bit divisor.
> 
> Also ensure that divide-by-zero (with fixed_rate as denominator) does
> not happen with an explicit check with probe failure as a consequence.
> 
> Cc: Michael Turquette <mturquette@...libre.com>
> Cc: Stephen Boyd <sboyd@...nel.org>
> Cc: linux-clk@...r.kernel.org
> 
> Signed-off-by: Guru Das Srinagesh <gurus@...eaurora.org>
> ---
>  drivers/clk/clk-pwm.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk-pwm.c b/drivers/clk/clk-pwm.c
> index 87fe0b0e..86f2e2d 100644
> --- a/drivers/clk/clk-pwm.c
> +++ b/drivers/clk/clk-pwm.c
> @@ -89,7 +89,12 @@ static int clk_pwm_probe(struct platform_device *pdev)
>  	}
>  
>  	if (of_property_read_u32(node, "clock-frequency", &clk_pwm->fixed_rate))
> -		clk_pwm->fixed_rate = NSEC_PER_SEC / pargs.period;
> +		clk_pwm->fixed_rate = div64_u64(NSEC_PER_SEC, pargs.period);
> +
> +	if (!clk_pwm->fixed_rate) {
> +		dev_err(&pdev->dev, "fixed_rate cannot be zero\n");
> +		return -EINVAL;
> +	}
>  
>  	if (pargs.period != NSEC_PER_SEC / clk_pwm->fixed_rate &&
>  	    pargs.period != DIV_ROUND_UP(NSEC_PER_SEC, clk_pwm->fixed_rate)) {
> -- 

Hello Arnd, David:

Sorry, missed cc-ing you both to this patch while sending it out. Could
you please review it when you get a chance to?

Thank you.

Guru Das.