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From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: thierry.reding@gmail.com, linux-pwm@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org
Subject: pwm: rcar: improve calculation of divider
Date: Fri, 7 Dec 2018 22:49:32 +0100	[thread overview]
Message-ID: <20181207214932.xckuuarcka733v7y@pengutronix.de> (raw)
In-Reply-To: <1544171373-29618-1-git-send-email-yoshihiro.shimoda.uh@renesas.com>

Hello,

while looking at the driver I noticed another patch opportunity: In
rcar_pwm_get_clock_division() there is a loop:

	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;
	}

The value of div should be calculatable without a loop. Something like:

   divider = NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE;
   tmp = (unsigned long long)period_ns * clk_rate + (divider - 1);
   do_div(tmp, divider);
   div = ilog2(tmp - 1) + 1;

You might want to check if my maths are right, I didn't test.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K�nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

WARNING: multiple messages have this Message-ID (diff)
From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: thierry.reding@gmail.com, linux-pwm@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org
Subject: pwm: rcar: improve calculation of divider
Date: Fri, 7 Dec 2018 22:49:32 +0100	[thread overview]
Message-ID: <20181207214932.xckuuarcka733v7y@pengutronix.de> (raw)
In-Reply-To: <1544171373-29618-1-git-send-email-yoshihiro.shimoda.uh@renesas.com>

Hello,

while looking at the driver I noticed another patch opportunity: In
rcar_pwm_get_clock_division() there is a loop:

	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;
	}

The value of div should be calculatable without a loop. Something like:

   divider = NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE;
   tmp = (unsigned long long)period_ns * clk_rate + (divider - 1);
   do_div(tmp, divider);
   div = ilog2(tmp - 1) + 1;

You might want to check if my maths are right, I didn't test.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

  parent reply	other threads:[~2018-12-07 21:49 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-07  8:29 [PATCH 0/5] pwm: rcar: Add support "atomic" API and workaround Yoshihiro Shimoda
2018-12-07  8:29 ` [PATCH 1/5] pwm: rcar: add rcar_pwm_calc_counter() to calculate PWMCNT value only Yoshihiro Shimoda
2018-12-07  9:00   ` Uwe Kleine-König
2018-12-07  9:00     ` Uwe Kleine-König
2018-12-07  8:29 ` [PATCH 2/5] pwm: rcar: Add support "atomic" API Yoshihiro Shimoda
2018-12-07  9:07   ` Uwe Kleine-König
2018-12-07  9:07     ` Uwe Kleine-König
2018-12-07  9:57     ` Geert Uytterhoeven
2018-12-07 10:45       ` Uwe Kleine-König
2018-12-07 10:45         ` Uwe Kleine-König
2018-12-10  4:58         ` Yoshihiro Shimoda
2018-12-07  8:29 ` [PATCH 3/5] pwm: rcar: Use "atomic" API on rcar_pwm_resume() Yoshihiro Shimoda
2018-12-07  8:29 ` [PATCH 4/5] pwm: rcar: remove legacy APIs Yoshihiro Shimoda
2018-12-07  8:29 ` [PATCH 5/5] pwm: rcar: add workaround to output "pseudo" low level Yoshihiro Shimoda
2018-12-07  9:13   ` Uwe Kleine-König
2018-12-07  9:13     ` Uwe Kleine-König
2018-12-10  4:49     ` Yoshihiro Shimoda
2018-12-10  8:11       ` Uwe Kleine-König
2018-12-10  8:11         ` Uwe Kleine-König
2018-12-12  3:19         ` Yoshihiro Shimoda
2018-12-12  3:19           ` Yoshihiro Shimoda
2018-12-12  7:37           ` Uwe Kleine-König
2018-12-12  7:37             ` Uwe Kleine-König
2018-12-12 10:49             ` Yoshihiro Shimoda
2018-12-12 10:49               ` Yoshihiro Shimoda
2018-12-13  9:47     ` Yoshihiro Shimoda
2018-12-13  9:47       ` Yoshihiro Shimoda
2018-12-13  9:52       ` Uwe Kleine-König
2018-12-13  9:52         ` Uwe Kleine-König
2018-12-13 10:53         ` Yoshihiro Shimoda
2018-12-13 10:53           ` Yoshihiro Shimoda
2018-12-07 21:49 ` Uwe Kleine-König [this message]
2018-12-07 21:49   ` pwm: rcar: improve calculation of divider Uwe Kleine-König
2018-12-09 20:55   ` Laurent Pinchart
2018-12-10  5:09     ` Yoshihiro Shimoda
2018-12-10  8:04       ` Uwe Kleine-König
2018-12-10  8:04         ` Uwe Kleine-König
2018-12-12  3:13         ` Yoshihiro Shimoda
2018-12-12  3:13           ` Yoshihiro Shimoda
2018-12-09 22:48 ` [PATCH 0/5] pwm: rcar: Add support "atomic" API and workaround Laurent Pinchart

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