Linux-Renesas-SoC Archive on lore.kernel.org
 help / color / Atom feed
From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
To: thierry.reding@gmail.com
Cc: linux-pwm@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Subject: [PATCH v3 4/4] pwm: rcar: improve calculation of divider
Date: Wed,  9 Jan 2019 17:19:08 +0900
Message-ID: <1547021948-7664-5-git-send-email-yoshihiro.shimoda.uh@renesas.com> (raw)
In-Reply-To: <1547021948-7664-1-git-send-email-yoshihiro.shimoda.uh@renesas.com>

The rcar_pwm_get_clock_division() has a loop to calculate the divider,
but the value of div should be calculatable without a loop. So,
this patch improves it.

This algorithm is suggested by Uwe Kleine-König and Laurent Pinchart.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
 drivers/pwm/pwm-rcar.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/pwm/pwm-rcar.c b/drivers/pwm/pwm-rcar.c
index 1e13fbb..cfe7dd1 100644
--- a/drivers/pwm/pwm-rcar.c
+++ b/drivers/pwm/pwm-rcar.c
@@ -8,6 +8,8 @@
 #include <linux/clk.h>
 #include <linux/err.h>
 #include <linux/io.h>
+#include <linux/log2.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -68,19 +70,15 @@ static void rcar_pwm_update(struct rcar_pwm_chip *rp, u32 mask, u32 data,
 static int rcar_pwm_get_clock_division(struct rcar_pwm_chip *rp, int period_ns)
 {
 	unsigned long clk_rate = clk_get_rate(rp->clk);
-	unsigned long long max; /* max cycle / nanoseconds */
-	unsigned int div;
+	u64 div, tmp;
 
 	if (clk_rate == 0)
 		return -EINVAL;
 
-	for (div = 0; div <= RCAR_PWM_MAX_DIVISION; div++) {
-		max = (unsigned long long)NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE *
-			(1 << div);
-		do_div(max, clk_rate);
-		if (period_ns <= max)
-			break;
-	}
+	div = (u64)NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE;
+	tmp = (u64)period_ns * clk_rate + div - 1;
+	tmp = div64_u64(tmp, div);
+	div = ilog2(tmp - 1) + 1;
 
 	return (div <= RCAR_PWM_MAX_DIVISION) ? div : -ERANGE;
 }
-- 
1.9.1


  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09  8:19 [PATCH v3 0/4] pwm: rcar: Add support "atomic" API and improve calculation Yoshihiro Shimoda
2019-01-09  8:19 ` [PATCH v3 1/4] pwm: rcar: Add support "atomic" API Yoshihiro Shimoda
2019-01-09  8:19 ` [PATCH v3 2/4] pwm: rcar: Use "atomic" API on rcar_pwm_resume() Yoshihiro Shimoda
2019-03-04 11:18   ` Thierry Reding
2019-01-09  8:19 ` [PATCH v3 3/4] pwm: rcar: remove legacy APIs Yoshihiro Shimoda
2019-01-09  8:19 ` Yoshihiro Shimoda [this message]
2019-03-04 11:14 ` [PATCH v3 0/4] pwm: rcar: Add support "atomic" API and improve calculation Thierry Reding

Reply instructions:

You may reply publically 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=1547021948-7664-5-git-send-email-yoshihiro.shimoda.uh@renesas.com \
    --to=yoshihiro.shimoda.uh@renesas.com \
    --cc=linux-pwm@vger.kernel.org \
    --cc=linux-renesas-soc@vger.kernel.org \
    --cc=thierry.reding@gmail.com \
    /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

Linux-Renesas-SoC Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-renesas-soc/0 linux-renesas-soc/git/0.git

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


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


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