From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: cgel.zte@gmail.com
Cc: thierry.reding@gmail.com, lee.jones@linaro.org,
nicolas.ferre@microchip.com, alexandre.belloni@bootlin.com,
ludovic.desroches@microchip.com, linux-pwm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Changcheng Deng <deng.changcheng@zte.com.cn>,
Zeal Robot <zealci@zte.com.cn>
Subject: Re: [PATCH] pwm: Use div64_ul instead of do_div
Date: Wed, 17 Nov 2021 12:24:00 +0100 [thread overview]
Message-ID: <20211117112400.bkscb2pyavonpfsn@pengutronix.de> (raw)
In-Reply-To: <20211117020426.159242-1-deng.changcheng@zte.com.cn>
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Hello,
On Wed, Nov 17, 2021 at 02:04:26AM +0000, cgel.zte@gmail.com wrote:
> From: Changcheng Deng <deng.changcheng@zte.com.cn>
>
> do_div() does a 64-by-32 division. If the divisor is unsigned long, using
> div64_ul can avoid truncation to 32-bit.
After some research I understood your commit log. I'd write:
do_div() does a 64-by-32 division. Here the divsor is an
unsigned long which on some platforms is 64 bit wide. So use
div64_ul instead of do_div to avoid a possible truncation.
The priority of this patch seems to be low, as the device seems to exist
only on (32bit) arm.
> diff --git a/drivers/pwm/pwm-atmel-hlcdc.c b/drivers/pwm/pwm-atmel-hlcdc.c
> index a43b2babc809..1ae3d73b9832 100644
> --- a/drivers/pwm/pwm-atmel-hlcdc.c
> +++ b/drivers/pwm/pwm-atmel-hlcdc.c
> @@ -60,7 +60,7 @@ static int atmel_hlcdc_pwm_apply(struct pwm_chip *c, struct pwm_device *pwm,
> return -EINVAL;
>
> clk_period_ns = (u64)NSEC_PER_SEC * 256;
> - do_div(clk_period_ns, clk_freq);
> + div64_ul(clk_period_ns, clk_freq);
This must be
clk_period_ns = div64_ul(clk_period_ns, clk_freq);
as div64_ul has a different calling convention than do_div. Same problem
in the next hunk.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2021-11-17 11:24 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-17 2:04 [PATCH] pwm: Use div64_ul instead of do_div cgel.zte
2021-11-17 11:24 ` Uwe Kleine-König [this message]
2021-11-17 12:46 ` [PATCH V2] " cgel.zte
2021-11-17 14:54 ` Uwe Kleine-König
2021-11-18 2:52 ` [PATCH V3] " cgel.zte
2021-11-18 9:54 ` Uwe Kleine-König
2021-11-18 10:09 ` [PATCH] " Russell King (Oracle)
2021-11-18 13:19 ` Nicolas Ferre
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