tegra: pwm: Allow the clock rate to be left as is

When enabling a PWM, allow the existing clock rate and source to stand
unchanged.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>

arch/arm/include/asm/arch-tegra/pwm.h

@@ -31,7 +31,7 @@ struct pwm_ctlr {
  * Program the PWM with the given parameters.
  *
  * @param channel	PWM channel to update
- * @param rate		Clock rate to use for PWM
+ * @param rate		Clock rate to use for PWM, or 0 to leave alone
  * @param pulse_width	high pulse width: 0=always low, 1=1/256 pulse high,
  *			n = n/256 pulse high
  * @param freq_divider	frequency divider value (1 to use rate as is)

arch/arm/mach-tegra/pwm.c

@@ -24,7 +24,10 @@ void pwm_enable(unsigned channel, int rate, int pulse_width, int freq_divider)
 	assert(channel < PWM_NUM_CHANNELS);
 
 	/* TODO: Can we use clock_adjust_periph_pll_div() here? */
-	clock_start_periph_pll(PERIPH_ID_PWM, CLOCK_ID_SFROM32KHZ, rate);
+	if (rate) {
+		clock_start_periph_pll(PERIPH_ID_PWM, CLOCK_ID_SFROM32KHZ,
+				       rate);
+	}
 
 	reg = PWM_ENABLE_MASK;
 	reg |= pulse_width << PWM_WIDTH_SHIFT;