Exynos: Tidy up the pwm_config function in the exynos pwm driver

Some small fixes in the exynos pwm driver:

1. NS_IN_HZ is non-sensical since these are not compatible units. This
constant actually describes the number of nanoseconds in a second. Renamed it
to NS_IN_SEC. Also dropped the unnecessary parenthesis.
2. The variable "period" is not used to hold a period, it's used to hold a
frequency. Renamed it to "frequency".
3. tcmp is an unsigned value, so (tcmp < 0) will never be true and the if
which checks that condition will never execute. Also, there should be no
problem if the pwm never switches, so there's no reason to subtract one from
tcmp and therefore no reason to compare it against zero. Removed both ifs. If
they weren't removed, tcmp should be a signed value.
4. Add a check for a 0 period.

Test with command "sf probe 1:0; time sf read 40008000 0 1000".
Try with different numbers of bytes and see that sane values are obtained
Build and boot U-boot with this patch, backlight works properly.

Signed-off-by: Gabe Black <gabeblack@google.com>
Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

arch/arm/cpu/armv7/s5p-common/pwm.c

@@ -70,7 +70,7 @@ static unsigned long pwm_calc_tin(int pwm_id, unsigned long freq)
 	return tin_parent_rate / 16;
 }
 
-#define NS_IN_HZ (1000000000UL)
+#define NS_IN_SEC 1000000000UL
 
 int pwm_config(int pwm_id, int duty_ns, int period_ns)
 {
@@ -79,7 +79,7 @@ int pwm_config(int pwm_id, int duty_ns, int period_ns)
 	unsigned int offset;
 	unsigned long tin_rate;
 	unsigned long tin_ns;
-	unsigned long period;
+	unsigned long frequency;
 	unsigned long tcon;
 	unsigned long tcnt;
 	unsigned long tcmp;
@@ -89,34 +89,24 @@ int pwm_config(int pwm_id, int duty_ns, int period_ns)
 	 * fact that anything faster than 1GHz is easily representable
 	 * by 32bits.
 	 */
-	if (period_ns > NS_IN_HZ || duty_ns > NS_IN_HZ)
+	if (period_ns > NS_IN_SEC || duty_ns > NS_IN_SEC || period_ns == 0)
 		return -ERANGE;
 
 	if (duty_ns > period_ns)
 		return -EINVAL;
 
-	period = NS_IN_HZ / period_ns;
+	frequency = NS_IN_SEC / period_ns;
 
 	/* Check to see if we are changing the clock rate of the PWM */
-	tin_rate = pwm_calc_tin(pwm_id, period);
+	tin_rate = pwm_calc_tin(pwm_id, frequency);
 
-	tin_ns = NS_IN_HZ / tin_rate;
+	tin_ns = NS_IN_SEC / tin_rate;
 	tcnt = period_ns / tin_ns;
 
 	/* Note, counters count down */
 	tcmp = duty_ns / tin_ns;
 	tcmp = tcnt - tcmp;
 
-	/*
-	 * the pwm hw only checks the compare register after a decrement,
-	 * so the pin never toggles if tcmp = tcnt
-	 */
-	if (tcmp == tcnt)
-		tcmp--;
-
-	if (tcmp < 0)
-		tcmp = 0;
-
 	/* Update the PWM register block. */
 	offset = pwm_id * 3;
 	if (pwm_id < 4) {