pwm: tegra: Read PWM clock source rate in driver init

It is required to know the PWM clock source frequency to calculate the
PWM period.

In driver, the clock source frequency of the PWM does not get change
and, hence, get the clock source frequency in driver init. Get this
values later for period calculation from pwm_config().

This will help in avoiding the clock call for getting clock rate in the
pwm_config() each time.
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-tegra.c

@@ -50,6 +50,8 @@ struct tegra_pwm_chip {
 	struct clk *clk;
 	struct reset_control*rst;
 
+	unsigned long clk_rate;
+
 	void __iomem *regs;
 
 	const struct tegra_pwm_soc *soc;
@@ -94,7 +96,7 @@ static int tegra_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	 * Compute the prescaler value for which (1 << PWM_DUTY_WIDTH)
 	 * cycles at the PWM clock rate will take period_ns nanoseconds.
 	 */
-	rate = clk_get_rate(pc->clk) >> PWM_DUTY_WIDTH;
+	rate = pc->clk_rate >> PWM_DUTY_WIDTH;
 
 	/* Consider precision in PWM_SCALE_WIDTH rate calculation */
 	hz = DIV_ROUND_CLOSEST_ULL(100ULL * NSEC_PER_SEC, period_ns);
@@ -199,6 +201,9 @@ static int tegra_pwm_probe(struct platform_device *pdev)
 	if (IS_ERR(pwm->clk))
 		return PTR_ERR(pwm->clk);
 
+	/* Read PWM clock rate from source */
+	pwm->clk_rate = clk_get_rate(pwm->clk);
+
 	pwm->rst = devm_reset_control_get(&pdev->dev, "pwm");
 	if (IS_ERR(pwm->rst)) {
 		ret = PTR_ERR(pwm->rst);