path: root/drivers/pwm/pwm-samsung.c
diff options
authorSjoerd Simons <sjoerd.simons@collabora.co.uk>2015-03-05 09:14:03 +0100
committerThierry Reding <thierry.reding@gmail.com>2015-03-27 13:06:47 +0100
commit4a1c683c98e4e2997c79258bffbb9be4af4fba83 (patch)
tree305543fa7a9731704c71d52e62be572d71355618 /drivers/pwm/pwm-samsung.c
parent24ccea1ce6717b91bb1e71b12cfd956f8d32dcf3 (diff)
pwm: samsung: Fix output race on disabling
When disabling the Samsung PWM the output state remains at the level it was at the end of a PWM cycle. In other words, calling pwm_disable() when at 100% duty cycle will keep the output active, while at all other settings the output will go/stay inactive. On top of that the Samsung PWM settings are double-buffered, which means the new settings only get applied at the start of a new PWM cycle. This results in a race if the PWM is at 100% duty cycle and a driver calls: pwm_config(pwm, 0, period); pwm_disable(pwm); In this case the PWMs output will unexpectedly stay active, unless a new PWM cycle happened to start between the register writes in pwm_config() and pwm_disable(). As far as I can tell this is a regression introduced by 3bdf878, before that a call to pwm_config() would call pwm_samsung_enable() which, while heavy-handed, made sure the expected settings were live. To resolve this, while not re-introducing the issues 3bdf878 (flickering as the PWM got reset while in a PWM cycle) fixed, only force an update of the settings when at 100% duty cycle, which shouldn't have any noticeable effect on the output but is enough to ensure the behaviour is as expected on disable. Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk> Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk> Acked-by: Lukasz Majewski <l.majewski@samsung.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm/pwm-samsung.c')
1 files changed, 31 insertions, 1 deletions
diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
index 3e9b5835a4af..ff201e1b9219 100644
--- a/drivers/pwm/pwm-samsung.c
+++ b/drivers/pwm/pwm-samsung.c
@@ -269,12 +269,31 @@ static void pwm_samsung_disable(struct pwm_chip *chip, struct pwm_device *pwm)
spin_unlock_irqrestore(&samsung_pwm_lock, flags);
+static void pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
+ struct pwm_device *pwm)
+ unsigned int tcon_chan = to_tcon_channel(pwm->hwpwm);
+ u32 tcon;
+ unsigned long flags;
+ spin_lock_irqsave(&samsung_pwm_lock, flags);
+ tcon = readl(chip->base + REG_TCON);
+ tcon |= TCON_MANUALUPDATE(tcon_chan);
+ writel(tcon, chip->base + REG_TCON);
+ tcon &= ~TCON_MANUALUPDATE(tcon_chan);
+ writel(tcon, chip->base + REG_TCON);
+ spin_unlock_irqrestore(&samsung_pwm_lock, flags);
static int pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm,
int duty_ns, int period_ns)
struct samsung_pwm_chip *our_chip = to_samsung_pwm_chip(chip);
struct samsung_pwm_channel *chan = pwm_get_chip_data(pwm);
- u32 tin_ns = chan->tin_ns, tcnt, tcmp;
+ u32 tin_ns = chan->tin_ns, tcnt, tcmp, oldtcmp;
* We currently avoid using 64bit arithmetic by using the
@@ -288,6 +307,7 @@ static int pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm,
return 0;
tcnt = readl(our_chip->base + REG_TCNTB(pwm->hwpwm));
+ oldtcmp = readl(our_chip->base + REG_TCMPB(pwm->hwpwm));
/* We need tick count for calculation, not last tick. */
@@ -335,6 +355,16 @@ static int pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm,
writel(tcnt, our_chip->base + REG_TCNTB(pwm->hwpwm));
writel(tcmp, our_chip->base + REG_TCMPB(pwm->hwpwm));
+ /*
+ * In case the PWM is currently at 100% duty cycle, force a manual
+ * update to prevent the signal staying high if the PWM is disabled
+ * shortly afer this update (before it autoreloaded the new values).
+ */
+ if (oldtcmp == (u32) -1) {
+ dev_dbg(our_chip->chip.dev, "Forcing manual update");
+ pwm_samsung_manual_update(our_chip, pwm);
+ }
chan->period_ns = period_ns;
chan->tin_ns = tin_ns;
chan->duty_ns = duty_ns;

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