pwm: rcar: improve calculation of divider

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

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

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Pengutronix e.K.                           | Uwe Kleine-König            |
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