ARM: S3C: PWM fix for low duty cycle

The pwm hardware only checks the compare register after a decrement,
so the pin never toggles if tcmp = tcnt.

This happens when a very low duty cycle is requested. Fix it by always
ensuring that tcmp < tcnt.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/arm/plat-s3c24xx/pwm.c b/arch/arm/plat-s3c24xx/pwm.c
index 0120b760315b..82a6d4de02a3 100644
--- a/arch/arm/plat-s3c24xx/pwm.c
+++ b/arch/arm/plat-s3c24xx/pwm.c
@@ -246,6 +246,10 @@ int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
 
         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--;
 
         pwm_dbg(pwm, "tin_ns=%lu, tcmp=%ld/%lu\n", tin_ns, tcmp, tcnt);