From: Andrew Bresticker <abrestic@xxxxxxxxxxxx>
When possible, avoid setting the manual update bit and starting/stopping
the PWM when adjusting the PWM as it causes noticable flickering when
setting the backlight brightness.
Signed-off-by: Andrew Bresticker <abrestic@xxxxxxxxxxxx>
Signed-off-by: Sachin Kamat <sachin.kamat@xxxxxxxxxx>
---
drivers/pwm/pwm-samsung.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
index b59639e..6d23eb3 100644
--- a/drivers/pwm/pwm-samsung.c
+++ b/drivers/pwm/pwm-samsung.c
@@ -34,6 +34,7 @@
#define REG_TCNTB(chan) (0x0c + ((chan) * 0xc))
#define REG_TCMPB(chan) (0x10 + ((chan) * 0xc))
+#define REG_TCNTO(chan) (0x14 + ((chan) * 0xc))
#define TCFG0_PRESCALER_MASK 0xff
#define TCFG0_PRESCALER1_SHIFT 8
@@ -234,15 +235,29 @@ static int pwm_samsung_enable(struct pwm_chip *chip, struct pwm_device *pwm)
struct samsung_pwm_chip *our_chip = to_samsung_pwm_chip(chip);
unsigned int tcon_chan = to_tcon_channel(pwm->hwpwm);
unsigned long flags;
- u32 tcon;
+ u32 tcon, tcnt, tcnt_o;
spin_lock_irqsave(&samsung_pwm_lock, flags);
tcon = readl(our_chip->base + REG_TCON);
+ tcnt = readl(our_chip->base + REG_TCNTB(pwm->hwpwm));
+ tcnt_o = readl(our_chip->base + REG_TCNTO(pwm->hwpwm));
- tcon &= ~TCON_START(tcon_chan);
- tcon |= TCON_MANUALUPDATE(tcon_chan);
- writel(tcon, our_chip->base + REG_TCON);
+ /*
+ * If we've got a big value stuck in the PWM we need to adjust it using
+ * manualupdate. The start bit needs to be off for that to work
+ * properly so we only do this if strictly necessary since it can cause
+ * the PWM to blink.
+ *
+ * We will also use manualupdate if we find that the autoreload bit
+ * wasn't set previously since the very first time the timer is
+ * configured we seem to need to kickstart the PWM.
+ */
+ if ((tcnt_o > tcnt) || !(tcon & TCON_AUTORELOAD(tcon_chan))) {
+ tcon &= ~TCON_START(tcon_chan);
+ tcon |= TCON_MANUALUPDATE(tcon_chan);
+ writel(tcon, our_chip->base + REG_TCON);
+ }
tcon &= ~TCON_MANUALUPDATE(tcon_chan);
tcon |= TCON_START(tcon_chan) | TCON_AUTORELOAD(tcon_chan);
--
1.7.9.5
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