diff options
author | Sjoerd Simons <sjoerd.simons@collabora.co.uk> | 2015-03-05 08:14:03 (GMT) |
---|---|---|
committer | Thierry Reding <thierry.reding@gmail.com> | 2015-03-27 12:06:47 (GMT) |
commit | 4a1c683c98e4e2997c79258bffbb9be4af4fba83 (patch) | |
tree | 305543fa7a9731704c71d52e62be572d71355618 /drivers | |
parent | 24ccea1ce6717b91bb1e71b12cfd956f8d32dcf3 (diff) | |
download | linux-4a1c683c98e4e2997c79258bffbb9be4af4fba83.tar.xz |
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')
-rw-r--r-- | drivers/pwm/pwm-samsung.c | 32 |
1 files changed, 31 insertions, 1 deletions
diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c index 3e9b583..ff201e1 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; |