pwm: rcar: Improve calculation of divider (b4f9a726) · Commits · 戴 / test

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> Signed-off-by:

Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-rcar.c

+7 −9

Original line number	Diff line number	Diff line
		@@ -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;
		}

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