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

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Message-ID: <20221110145320.fwrdsymdfpdjyyga@pengutronix.de>
Date:   Thu, 10 Nov 2022 15:53:20 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Steven Price <steven.price@....com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH] pwm: tegra: Fix 32 bit build

Hello,

On Thu, Nov 10, 2022 at 11:45:48AM +0000, 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.

Hmm, ideally this should have popped up earlier :-\

Anyhow:

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

Thanks
Uwe

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

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