| Message ID | 1427387955-5129-6-git-send-email-linux.amoon@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Anand, > From: Sjoerd Simons <sjoerd.simons@collabora.co.uk> > > When disabling the samsung PWM the output state remains at the level > it was in the end of a pwm cycle. In other words, calling pwm_disable > when at 100% duty will keep the output active, while at all other > setting 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 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 > _config and _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). Only force an > update of the settings when at 100% duty, which shouldn't have a > 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> > Signed-off-by: Anand Moon <linux.amoon@gmail.com> > --- > drivers/pwm/pwm-samsung.c | 31 ++++++++++++++++++++++++++++++- > 1 file changed, 30 insertions(+), 1 deletion(-) > > diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c > index 3e9b583..649f6c4 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 +355,15 @@ 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, force a manual > update Cosmetic comment: Wasn't checkpatch complaining about this comment style? /* ..... * ..... instead of: /* * ..... * ..... > + * to prevent the signal staying high in 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; Despite the above, Acked-by: Lukasz Majewski <l.majewski@samsung.com>
On Wed, 2015-04-08 at 10:28 +0200, Lukasz Majewski wrote: > Hi Anand, > > > From: Sjoerd Simons <sjoerd.simons@collabora.co.uk> > > When disabling the samsung PWM the output state remains at the level > > it was in the end of a pwm cycle. In other words, calling pwm_disable > > when at 100% duty will keep the output active, while at all other > > setting 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 patch is already in the linux-pwm for-next tree so should probably be dropped form this patchset to prevent conflicts.
Hi Sjoerd, Correct. Will do so. I just included in this series. As it relevant to my changes and testing. -Anand Moon On 8 April 2015 at 14:12, Sjoerd Simons <sjoerd.simons@collabora.co.uk> wrote: > > > On Wed, 2015-04-08 at 10:28 +0200, Lukasz Majewski wrote: >> Hi Anand, >> >> > From: Sjoerd Simons <sjoerd.simons@collabora.co.uk> >> > When disabling the samsung PWM the output state remains at the level >> > it was in the end of a pwm cycle. In other words, calling pwm_disable >> > when at 100% duty will keep the output active, while at all other >> > setting 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 patch is already in the linux-pwm for-next tree so should probably > be dropped form this patchset to prevent conflicts. > > -- > Sjoerd Simons <sjoerd.simons@collabora.co.uk> > Collabora Ltd. -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c index 3e9b583..649f6c4 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 +355,15 @@ 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, force a manual update + * to prevent the signal staying high in 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;