LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Guru Das Srinagesh <gurus@codeaurora.org>
To: Daniel Thompson <daniel.thompson@linaro.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 13:25:25 -0700
Message-ID: <20200521202525.GA24026@codeaurora.org> (raw)
In-Reply-To: <20200521101934.j5ivjky4e6byveut@holly.lan>

On Thu, May 21, 2020 at 11:19:34AM +0100, Daniel Thompson wrote:
> 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.

My initial patch [1] was to simply use DIV64_U64_ROUND_CLOSEST(), but I
got review feedback to add a short-circuit (same thread, [2]). I feel
like I should skip the short-circuiting and type casting and simply just
use DIV64_U64_ROUND_CLOSEST() - what do you think?

[1] https://lore.kernel.org/lkml/587f9ccae68ad7e1ce97fa8da6037292af1a5095.1584473399.git.gurus@codeaurora.org/
[2] https://lore.kernel.org/lkml/CAK8P3a2Hi_AoRC3g7qKth4e_Y1jZrbBDhWUb3YPZm10FWMu-ig@mail.gmail.com/

  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
2020-05-21 20:25     ` Guru Das Srinagesh [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200521202525.GA24026@codeaurora.org \
    --to=gurus@codeaurora.org \
    --cc=arnd@arndb.de \
    --cc=collinsd@codeaurora.org \
    --cc=dan.carpenter@oracle.com \
    --cc=daniel.thompson@linaro.org \
    --cc=geert@linux-m68k.org \
    --cc=joe@perches.com \
    --cc=lee.jones@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pwm@vger.kernel.org \
    --cc=linux@roeck-us.net \
    --cc=sboyd@kernel.org \
    --cc=subbaram@codeaurora.org \
    --cc=thierry.reding@gmail.com \
    --cc=u.kleine-koenig@pengutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git