linux-kernel - Re: [PATCH] pwm: tegra: Fix 32 bit build

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Date:   Thu, 10 Nov 2022 13:18:30 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Steven Price <steven.price@....com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH] pwm: tegra: Fix 32 bit build


On 10/11/2022 11:45, Steven Price wrote:
> The value of NSEC_PER_SEC << PWM_DUTY_WIDTH doesn't fix within a 32 bit
> integer causing a build warning/error (and the value truncated):
> 
>    drivers/pwm/pwm-tegra.c: In function ‘tegra_pwm_config’:
>    drivers/pwm/pwm-tegra.c:148:53: error: result of ‘1000000000 << 8’ requires 39 bits to represent, but ‘long int’ only has 32 bits [-Werror=shift-overflow=]
>      148 |   required_clk_rate = DIV_ROUND_UP_ULL(NSEC_PER_SEC << PWM_DUTY_WIDTH,
>          |                                                     ^~
> 
> Explicitly cast to a u64 to ensure the correct result.
> 
> Fixes: cfcb68817fb3 ("pwm: tegra: Improve required rate calculation")
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>   drivers/pwm/pwm-tegra.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c
> index 6fc4b69a3ba7..249dc0193297 100644
> --- a/drivers/pwm/pwm-tegra.c
> +++ b/drivers/pwm/pwm-tegra.c
> @@ -145,7 +145,7 @@ static int tegra_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>   		 * source clock rate as required_clk_rate, PWM controller will
>   		 * be able to configure the requested period.
>   		 */
> -		required_clk_rate = DIV_ROUND_UP_ULL(NSEC_PER_SEC << PWM_DUTY_WIDTH,
> +		required_clk_rate = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC << PWM_DUTY_WIDTH,
>   						     period_ns);
>   
>   		if (required_clk_rate > clk_round_rate(pc->clk, required_clk_rate))


Thanks!

Reviewed-by: Jon Hunter <jonathanh@...dia.com>

Jon

-- 
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