From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Guru Das Srinagesh <gurus@codeaurora.org>
Cc: "Linux PWM List" <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 Mailing List" <linux-kernel@vger.kernel.org>,
"Alexander Shiyan" <shc_work@mail.ru>,
"Arnd Bergmann" <arnd@arndb.de>
Subject: Re: [PATCH v13 04/11] pwm: clps711x: Cast period to u32 before use as divisor
Date: Thu, 23 Apr 2020 11:30:19 +0200 [thread overview]
Message-ID: <CAMuHMdVOPKWL9u_4QCvcBZKFrW-7aKZonXjODqUx9HwS=CF09g@mail.gmail.com> (raw)
In-Reply-To: <02ba64d8289bf84a8d140f5a3c38ed64a9474d3b.1587523702.git.gurus@codeaurora.org>
On Wed, Apr 22, 2020 at 5:00 AM Guru Das Srinagesh <gurus@codeaurora.org> 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.
>
> Cc: Alexander Shiyan <shc_work@mail.ru>
> Cc: Arnd Bergmann <arnd@arndb.de>
>
> 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..0d368ac 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 ((u32)pwm->args.period > (v * 0xf))
Shouldn't the cast be removed from the expression above?
Else a period larger than or equal to 2^32 may be accepted, but truncated
silently. And even cause a division by zero error.
> + return 0;
> +
> + return DIV_ROUND_CLOSEST(v * 0xf, (u32)pwm->args.period);
> }
>
> static int clps711x_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2020-04-23 9:30 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1587523702.git.gurus@codeaurora.org>
2020-04-22 2:57 ` [PATCH v13 01/11] drm/i915: Use 64-bit division macro Guru Das Srinagesh
2020-04-24 6:17 ` Jani Nikula
2020-04-24 22:17 ` Guru Das Srinagesh
2020-04-27 13:48 ` Jani Nikula
2020-04-22 2:57 ` [PATCH v13 02/11] hwmon: pwm-fan: " Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 03/11] ir-rx51: " Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 04/11] pwm: clps711x: Cast period to u32 before use as divisor Guru Das Srinagesh
2020-04-23 9:30 ` Geert Uytterhoeven [this message]
2020-04-24 22:21 ` Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 05/11] pwm: pwm-imx-tpm: Use 64-bit division macro Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 06/11] pwm: imx27: Use 64-bit division macro and function Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 07/11] pwm: sifive: Use 64-bit division macro Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 08/11] pwm: sun4i: Use nsecs_to_jiffies to avoid a division Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 09/11] backlight: pwm_bl: Use 64-bit division function Guru Das Srinagesh
2020-05-26 7:00 ` Lee Jones
2020-04-22 2:57 ` [PATCH v13 10/11] clk: pwm: " Guru Das Srinagesh
2020-04-22 2:57 ` [PATCH v13 11/11] pwm: core: Convert period and duty cycle to u64 Guru Das Srinagesh
2020-05-22 13:26 ` Uwe Kleine-König
[not found] ` <20200423114857.GG3612@dell>
[not found] ` <20200423215306.GA8670@codeaurora.org>
[not found] ` <20200424064303.GJ3612@dell>
[not found] ` <20200424221422.GA31118@codeaurora.org>
[not found] ` <20200427064434.GA3559@dell>
2020-05-20 23:15 ` [PATCH v13 00/11] Convert PWM " Guru Das Srinagesh
2020-05-21 7:15 ` Lee Jones
2020-05-22 11:16 ` Thierry Reding
2020-05-22 11:31 ` Lee Jones
2020-05-22 12:50 ` Thierry Reding
2020-05-22 22:59 ` Guru Das Srinagesh
2020-05-26 6:59 ` Lee Jones
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