From 4a1c683c98e4e2997c79258bffbb9be4af4fba83 Mon Sep 17 00:00:00 2001 From: Sjoerd Simons Date: Thu, 5 Mar 2015 09:14:03 +0100 Subject: 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 Reviewed-by: Javier Martinez Canillas Acked-by: Lukasz Majewski Signed-off-by: Thierry Reding --- drivers/pwm/pwm-samsung.c | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-) (limited to 'drivers/pwm') 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. */ ++tcnt; @@ -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; -- cgit v1.2.3