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From: Daniel Thompson <daniel.thompson@linaro.org>
To: Guru Das Srinagesh <gurus@codeaurora.org>
Cc: linux-pwm@vger.kernel.org,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Subbaraman Narayanamurthy" <subbaram@codeaurora.org>,
	"David Collins" <collinsd@codeaurora.org>,
	linux-kernel@vger.kernel.org, "Joe Perches" <joe@perches.com>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Lee Jones" <lee.jones@linaro.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>,
	"Guenter Roeck" <linux@roeck-us.net>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor
Date: Thu, 21 May 2020 11:19:34 +0100
Message-ID: <20200521101934.j5ivjky4e6byveut@holly.lan> (raw)
In-Reply-To: <1d6918c3fc2976bdbdb687bf54a2ef09fc1558db.1589330178.git.gurus@codeaurora.org>

On Wed, May 20, 2020 at 03:55:57PM -0700, Guru Das Srinagesh wrote:
> Since the PWM framework is switching struct pwm_args.period's datatype
> to u64, prepare for this transition by typecasting it to u32.
> 
> Also, since the dividend is still a 32-bit number, any divisor greater
> than the numerator will cause the quotient to be zero, so return 0 in
> that case to efficiently skip the division.
> 
> Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
> ---
>  drivers/pwm/pwm-clps711x.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c
> index 924d39a..da771b1 100644
> --- a/drivers/pwm/pwm-clps711x.c
> +++ b/drivers/pwm/pwm-clps711x.c
> @@ -43,7 +43,10 @@ static void clps711x_pwm_update_val(struct clps711x_chip *priv, u32 n, u32 v)
>  static unsigned int clps711x_get_duty(struct pwm_device *pwm, unsigned int v)
>  {
>  	/* Duty cycle 0..15 max */
> -	return DIV_ROUND_CLOSEST(v * 0xf, pwm->args.period);
> +	if (pwm->args.period > (v * 0xf))
> +		return 0;

This doesn't look right to me.

DIV_ROUND_CLOSEST() does rounded division and the short circuit doesn't
implement that.


Daniel.

> +
> +	return DIV_ROUND_CLOSEST(v * 0xf, (u32)pwm->args.period);
>  }
>  
>  static int clps711x_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 

  parent reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13  0:39 [RESEND PATCH v14 00/11] Convert PWM period and duty cycle to u64 Guru Das Srinagesh
2020-05-04 18:50 ` Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 01/11] drm/i915: Use 64-bit division macro Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 02/11] hwmon: pwm-fan: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 03/11] ir-rx51: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 05/11] pwm: pwm-imx-tpm: Use 64-bit division macro Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 06/11] pwm: imx27: Use 64-bit division macro and function Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 07/11] pwm: sifive: Use 64-bit division macro Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 08/11] pwm: sun4i: Use nsecs_to_jiffies to avoid a division Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 09/11] backlight: pwm_bl: Use 64-bit division function Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 10/11] clk: pwm: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 11/11] pwm: core: Convert period and duty cycle to u64 Guru Das Srinagesh
2020-05-13  0:39   ` [RESEND PATCH v14 00/11] Convert PWM " Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 01/11] drm/i915: Use 64-bit division macro Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 02/11] hwmon: pwm-fan: " Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 03/11] ir-rx51: " Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-21 10:19   ` Daniel Thompson [this message]
2020-05-21 20:25     ` Guru Das Srinagesh
2020-05-22  9:37       ` Daniel Thompson
2020-05-22 23:19         ` Guru Das Srinagesh
2020-05-23 17:08           ` Daniel Thompson
2020-05-13  0:39 ` [RESEND PATCH v14 05/11] pwm: pwm-imx-tpm: Use 64-bit division macro Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 06/11] pwm: imx27: Use 64-bit division macro and function Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 07/11] pwm: sifive: Use 64-bit division macro Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 08/11] pwm: sun4i: Use nsecs_to_jiffies to avoid a division Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 09/11] backlight: pwm_bl: Use 64-bit division function Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 10/11] clk: pwm: " Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 11/11] pwm: core: Convert period and duty cycle to u64 Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-20 22:55 ` [RESEND PATCH v14 00/11] Convert PWM " Guru Das Srinagesh

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