Initially this was designed to:
| Fix sleeping in atomic context warning and a deadlock after iio_trigger_poll()
| call
|
| If iio_trigger_poll() is called after IRQ was disabled, we will call
| reenable_trigger() directly from hard IRQ or hrtimer context instead of
| IRQ thread. In this case we will run in to multiple issue as sleeping in atomic
| context and a deadlock.
|
| To avoid this issue, rework the trigger to use state machine. All state
| changes are done over the hrtimer, so it allows us to drop fsleep() and
| avoid the deadlock.
This issue was fixed by: 9020ef659885 ("iio: trigger: Fix a scheduling
whilst atomic issue seen on tsc2046").
Even if the root cause of this issue probably will and can be fixed in the iio
core, this patch can be seen as clean-up to provide better internal state
machine.
Fixes: 9374e8f5a38d ("iio: adc: add ADC driver for the TI TSC2046 controller")
Signed-off-by: Oleksij Rempel <[email protected]>
---
drivers/iio/adc/ti-tsc2046.c | 102 ++++++++++++++++++++---------------
1 file changed, 58 insertions(+), 44 deletions(-)
diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
index d84ae6b008c1..91f6bd5effe7 100644
--- a/drivers/iio/adc/ti-tsc2046.c
+++ b/drivers/iio/adc/ti-tsc2046.c
@@ -123,14 +123,21 @@ struct tsc2046_adc_ch_cfg {
unsigned int oversampling_ratio;
};
+enum tsc2046_state {
+ TSC2046_STATE_STANDBY,
+ TSC2046_STATE_ENABLE_IRQ_POLL,
+ TSC2046_STATE_POLL,
+ TSC2046_STATE_ENABLE_IRQ,
+};
+
struct tsc2046_adc_priv {
struct spi_device *spi;
const struct tsc2046_adc_dcfg *dcfg;
struct iio_trigger *trig;
struct hrtimer trig_timer;
- spinlock_t trig_lock;
- unsigned int trig_more_count;
+ enum tsc2046_state state;
+ spinlock_t state_lock;
struct spi_transfer xfer;
struct spi_message msg;
@@ -411,21 +418,47 @@ static const struct iio_info tsc2046_adc_info = {
.update_scan_mode = tsc2046_adc_update_scan_mode,
};
-static enum hrtimer_restart tsc2046_adc_trig_more(struct hrtimer *hrtimer)
+static enum hrtimer_restart tsc2046_adc_timer(struct hrtimer *hrtimer)
{
struct tsc2046_adc_priv *priv = container_of(hrtimer,
struct tsc2046_adc_priv,
trig_timer);
unsigned long flags;
- spin_lock_irqsave(&priv->trig_lock, flags);
-
- disable_irq_nosync(priv->spi->irq);
-
- priv->trig_more_count++;
- iio_trigger_poll(priv->trig);
-
- spin_unlock_irqrestore(&priv->trig_lock, flags);
+ spin_lock_irqsave(&priv->state_lock, flags);
+ switch (priv->state) {
+ case TSC2046_STATE_ENABLE_IRQ_POLL:
+ /*
+ * IRQ handler called iio_trigger_poll() to sample ADC.
+ * Here we
+ * - re-enable IRQs
+ * - start hrtimer for timeout if no IRQ will occur
+ */
+ priv->state = TSC2046_STATE_POLL;
+ enable_irq(priv->spi->irq);
+ hrtimer_start(&priv->trig_timer,
+ ns_to_ktime(priv->scan_interval_us *
+ NSEC_PER_USEC),
+ HRTIMER_MODE_REL_SOFT);
+ break;
+ case TSC2046_STATE_POLL:
+ disable_irq_nosync(priv->spi->irq);
+ priv->state = TSC2046_STATE_ENABLE_IRQ;
+ /* iio_trigger_poll() starts hrtimer */
+ iio_trigger_poll(priv->trig);
+ break;
+ case TSC2046_STATE_ENABLE_IRQ:
+ priv->state = TSC2046_STATE_STANDBY;
+ enable_irq(priv->spi->irq);
+ break;
+ case TSC2046_STATE_STANDBY:
+ fallthrough;
+ default:
+ dev_warn(&priv->spi->dev, "Got unexpected state: %i\n",
+ priv->state);
+ break;
+ }
+ spin_unlock_irqrestore(&priv->state_lock, flags);
return HRTIMER_NORESTART;
}
@@ -434,16 +467,17 @@ static irqreturn_t tsc2046_adc_irq(int irq, void *dev_id)
{
struct iio_dev *indio_dev = dev_id;
struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
-
- spin_lock(&priv->trig_lock);
+ unsigned long flags;
hrtimer_try_to_cancel(&priv->trig_timer);
- priv->trig_more_count = 0;
+ spin_lock_irqsave(&priv->state_lock, flags);
disable_irq_nosync(priv->spi->irq);
- iio_trigger_poll(priv->trig);
+ priv->state = TSC2046_STATE_ENABLE_IRQ_POLL;
- spin_unlock(&priv->trig_lock);
+ /* iio_trigger_poll() starts hrtimer */
+ iio_trigger_poll(priv->trig);
+ spin_unlock_irqrestore(&priv->state_lock, flags);
return IRQ_HANDLED;
}
@@ -452,37 +486,16 @@ static void tsc2046_adc_reenable_trigger(struct iio_trigger *trig)
{
struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
- unsigned long flags;
- int delta;
+ ktime_t tim;
/*
* We can sample it as fast as we can, but usually we do not need so
* many samples. Reduce the sample rate for default (touchscreen) use
* case.
- * Currently we do not need a highly precise sample rate. It is enough
- * to have calculated numbers.
- */
- delta = priv->scan_interval_us - priv->time_per_scan_us;
- if (delta > 0)
- fsleep(delta);
-
- spin_lock_irqsave(&priv->trig_lock, flags);
-
- /*
- * We need to trigger at least one extra sample to detect state
- * difference on ADC side.
*/
- if (!priv->trig_more_count) {
- int timeout_ms = DIV_ROUND_UP(priv->scan_interval_us,
- USEC_PER_MSEC);
-
- hrtimer_start(&priv->trig_timer, ms_to_ktime(timeout_ms),
- HRTIMER_MODE_REL_SOFT);
- }
-
- enable_irq(priv->spi->irq);
-
- spin_unlock_irqrestore(&priv->trig_lock, flags);
+ tim = ns_to_ktime((priv->scan_interval_us - priv->time_per_scan_us) *
+ NSEC_PER_USEC);
+ hrtimer_start(&priv->trig_timer, tim, HRTIMER_MODE_REL_SOFT);
}
static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
@@ -493,8 +506,8 @@ static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
if (enable) {
enable_irq(priv->spi->irq);
} else {
+ hrtimer_cancel(&priv->trig_timer);
disable_irq(priv->spi->irq);
- hrtimer_try_to_cancel(&priv->trig_timer);
}
return 0;
@@ -668,10 +681,11 @@ static int tsc2046_adc_probe(struct spi_device *spi)
iio_trigger_set_drvdata(trig, indio_dev);
trig->ops = &tsc2046_adc_trigger_ops;
- spin_lock_init(&priv->trig_lock);
+ spin_lock_init(&priv->state_lock);
+ priv->state = TSC2046_STATE_STANDBY;
hrtimer_init(&priv->trig_timer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL_SOFT);
- priv->trig_timer.function = tsc2046_adc_trig_more;
+ priv->trig_timer.function = tsc2046_adc_timer;
ret = devm_iio_trigger_register(dev, trig);
if (ret) {
--
2.30.2
On Fri, 7 Jan 2022 08:40:17 +0100
Oleksij Rempel <[email protected]> wrote:
> Initially this was designed to:
> | Fix sleeping in atomic context warning and a deadlock after iio_trigger_poll()
> | call
> |
> | If iio_trigger_poll() is called after IRQ was disabled, we will call
> | reenable_trigger() directly from hard IRQ or hrtimer context instead of
> | IRQ thread. In this case we will run in to multiple issue as sleeping in atomic
> | context and a deadlock.
> |
> | To avoid this issue, rework the trigger to use state machine. All state
> | changes are done over the hrtimer, so it allows us to drop fsleep() and
> | avoid the deadlock.
>
> This issue was fixed by: 9020ef659885 ("iio: trigger: Fix a scheduling
> whilst atomic issue seen on tsc2046").
>
> Even if the root cause of this issue probably will and can be fixed in the iio
> core, this patch can be seen as clean-up to provide better internal state
> machine.
Probably want to update this text?
A few comments below.
>
> Fixes: 9374e8f5a38d ("iio: adc: add ADC driver for the TI TSC2046 controller")
From above isn't this now fixed? The cleanup here is just making things easier
to follow I think...
> Signed-off-by: Oleksij Rempel <[email protected]>
> ---
> drivers/iio/adc/ti-tsc2046.c | 102 ++++++++++++++++++++---------------
> 1 file changed, 58 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
> index d84ae6b008c1..91f6bd5effe7 100644
> --- a/drivers/iio/adc/ti-tsc2046.c
> +++ b/drivers/iio/adc/ti-tsc2046.c
> @@ -123,14 +123,21 @@ struct tsc2046_adc_ch_cfg {
> unsigned int oversampling_ratio;
> };
>
> +enum tsc2046_state {
> + TSC2046_STATE_STANDBY,
> + TSC2046_STATE_ENABLE_IRQ_POLL,
> + TSC2046_STATE_POLL,
> + TSC2046_STATE_ENABLE_IRQ,
> +};
> +
> struct tsc2046_adc_priv {
> struct spi_device *spi;
> const struct tsc2046_adc_dcfg *dcfg;
>
> struct iio_trigger *trig;
> struct hrtimer trig_timer;
> - spinlock_t trig_lock;
> - unsigned int trig_more_count;
> + enum tsc2046_state state;
> + spinlock_t state_lock;
>
> struct spi_transfer xfer;
> struct spi_message msg;
> @@ -411,21 +418,47 @@ static const struct iio_info tsc2046_adc_info = {
> .update_scan_mode = tsc2046_adc_update_scan_mode,
> };
>
> -static enum hrtimer_restart tsc2046_adc_trig_more(struct hrtimer *hrtimer)
> +static enum hrtimer_restart tsc2046_adc_timer(struct hrtimer *hrtimer)
> {
> struct tsc2046_adc_priv *priv = container_of(hrtimer,
> struct tsc2046_adc_priv,
> trig_timer);
> unsigned long flags;
>
> - spin_lock_irqsave(&priv->trig_lock, flags);
> -
> - disable_irq_nosync(priv->spi->irq);
> -
> - priv->trig_more_count++;
> - iio_trigger_poll(priv->trig);
> -
> - spin_unlock_irqrestore(&priv->trig_lock, flags);
> + spin_lock_irqsave(&priv->state_lock, flags);
> + switch (priv->state) {
> + case TSC2046_STATE_ENABLE_IRQ_POLL:
> + /*
> + * IRQ handler called iio_trigger_poll() to sample ADC.
> + * Here we
> + * - re-enable IRQs
> + * - start hrtimer for timeout if no IRQ will occur
> + */
> + priv->state = TSC2046_STATE_POLL;
> + enable_irq(priv->spi->irq);
I comment on this below, but I'm not sure why you don't move the enable_irq()
here out of this timer function and then have the first entry of the timer
go directly to TSC2046_STATE_POLL after a longer initial wait.
It's been a long time since I looked at this, so perhaps I'm missing the
point. What you have here works as far as I can see, it just seems to push
more than necessary into the state machine.
> + hrtimer_start(&priv->trig_timer,
> + ns_to_ktime(priv->scan_interval_us *
> + NSEC_PER_USEC),
> + HRTIMER_MODE_REL_SOFT);
> + break;
> + case TSC2046_STATE_POLL:
> + disable_irq_nosync(priv->spi->irq);
> + priv->state = TSC2046_STATE_ENABLE_IRQ;
> + /* iio_trigger_poll() starts hrtimer */
> + iio_trigger_poll(priv->trig);
> + break;
> + case TSC2046_STATE_ENABLE_IRQ:
> + priv->state = TSC2046_STATE_STANDBY;
> + enable_irq(priv->spi->irq);
> + break;
> + case TSC2046_STATE_STANDBY:
> + fallthrough;
> + default:
> + dev_warn(&priv->spi->dev, "Got unexpected state: %i\n",
> + priv->state);
> + break;
> + }
> + spin_unlock_irqrestore(&priv->state_lock, flags);
>
> return HRTIMER_NORESTART;
> }
> @@ -434,16 +467,17 @@ static irqreturn_t tsc2046_adc_irq(int irq, void *dev_id)
> {
> struct iio_dev *indio_dev = dev_id;
> struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
> -
> - spin_lock(&priv->trig_lock);
> + unsigned long flags;
>
> hrtimer_try_to_cancel(&priv->trig_timer);
>
> - priv->trig_more_count = 0;
> + spin_lock_irqsave(&priv->state_lock, flags);x`
> disable_irq_nosync(priv->spi->irq);
> - iio_trigger_poll(priv->trig);
> + priv->state = TSC2046_STATE_ENABLE_IRQ_POLL;
>
> - spin_unlock(&priv->trig_lock);
> + /* iio_trigger_poll() starts hrtimer */
> + iio_trigger_poll(priv->trig);
> + spin_unlock_irqrestore(&priv->state_lock, flags);
>
> return IRQ_HANDLED;
> }
> @@ -452,37 +486,16 @@ static void tsc2046_adc_reenable_trigger(struct iio_trigger *trig)
> {
> struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
> struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
> - unsigned long flags;
> - int delta;
> + ktime_t tim;
>
> /*
> * We can sample it as fast as we can, but usually we do not need so
> * many samples. Reduce the sample rate for default (touchscreen) use
> * case.
> - * Currently we do not need a highly precise sample rate. It is enough
> - * to have calculated numbers.
> - */
> - delta = priv->scan_interval_us - priv->time_per_scan_us;
> - if (delta > 0)
> - fsleep(delta);
> -
> - spin_lock_irqsave(&priv->trig_lock, flags);
> -
> - /*
> - * We need to trigger at least one extra sample to detect state
> - * difference on ADC side.
> */
> - if (!priv->trig_more_count) {
> - int timeout_ms = DIV_ROUND_UP(priv->scan_interval_us,
> - USEC_PER_MSEC);
> -
> - hrtimer_start(&priv->trig_timer, ms_to_ktime(timeout_ms),
> - HRTIMER_MODE_REL_SOFT);
> - }
> -
> - enable_irq(priv->spi->irq);
> -
> - spin_unlock_irqrestore(&priv->trig_lock, flags);
> + tim = ns_to_ktime((priv->scan_interval_us - priv->time_per_scan_us) *
> + NSEC_PER_USEC);
> + hrtimer_start(&priv->trig_timer, tim, HRTIMER_MODE_REL_SOFT);
This moves enabling the irq to the first instance of the timer - is that ever too late?
> }
>
> static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
> @@ -493,8 +506,8 @@ static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
> if (enable) {
> enable_irq(priv->spi->irq);
> } else {
> + hrtimer_cancel(&priv->trig_timer);
So this will wait for the callback to finish. However, is there a chance
of an interrupt just after this but before disable_irq that ends up
starting the timer again?
> disable_irq(priv->spi->irq);
> - hrtimer_try_to_cancel(&priv->trig_timer);
> }
>
> return 0;
> @@ -668,10 +681,11 @@ static int tsc2046_adc_probe(struct spi_device *spi)
> iio_trigger_set_drvdata(trig, indio_dev);
> trig->ops = &tsc2046_adc_trigger_ops;
>
> - spin_lock_init(&priv->trig_lock);
> + spin_lock_init(&priv->state_lock);
> + priv->state = TSC2046_STATE_STANDBY;
> hrtimer_init(&priv->trig_timer, CLOCK_MONOTONIC,
> HRTIMER_MODE_REL_SOFT);
> - priv->trig_timer.function = tsc2046_adc_trig_more;
> + priv->trig_timer.function = tsc2046_adc_timer;
>
> ret = devm_iio_trigger_register(dev, trig);
> if (ret) {
On Sun, Jan 09, 2022 at 03:44:04PM +0000, Jonathan Cameron wrote:
> On Fri, 7 Jan 2022 08:40:17 +0100
> Oleksij Rempel <[email protected]> wrote:
>
> > Initially this was designed to:
> > | Fix sleeping in atomic context warning and a deadlock after iio_trigger_poll()
> > | call
> > |
> > | If iio_trigger_poll() is called after IRQ was disabled, we will call
> > | reenable_trigger() directly from hard IRQ or hrtimer context instead of
> > | IRQ thread. In this case we will run in to multiple issue as sleeping in atomic
> > | context and a deadlock.
> > |
> > | To avoid this issue, rework the trigger to use state machine. All state
> > | changes are done over the hrtimer, so it allows us to drop fsleep() and
> > | avoid the deadlock.
> >
> > This issue was fixed by: 9020ef659885 ("iio: trigger: Fix a scheduling
> > whilst atomic issue seen on tsc2046").
> >
> > Even if the root cause of this issue probably will and can be fixed in the iio
> > core, this patch can be seen as clean-up to provide better internal state
> > machine.
>
> Probably want to update this text?
ack
> A few comments below.
> >
> > Fixes: 9374e8f5a38d ("iio: adc: add ADC driver for the TI TSC2046 controller")
>
> From above isn't this now fixed? The cleanup here is just making things easier
> to follow I think...
done
> > Signed-off-by: Oleksij Rempel <[email protected]>
> > ---
> > drivers/iio/adc/ti-tsc2046.c | 102 ++++++++++++++++++++---------------
> > 1 file changed, 58 insertions(+), 44 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
> > index d84ae6b008c1..91f6bd5effe7 100644
> > --- a/drivers/iio/adc/ti-tsc2046.c
> > +++ b/drivers/iio/adc/ti-tsc2046.c
> > @@ -123,14 +123,21 @@ struct tsc2046_adc_ch_cfg {
> > unsigned int oversampling_ratio;
> > };
> >
> > +enum tsc2046_state {
> > + TSC2046_STATE_STANDBY,
> > + TSC2046_STATE_ENABLE_IRQ_POLL,
> > + TSC2046_STATE_POLL,
> > + TSC2046_STATE_ENABLE_IRQ,
> > +};
> > +
> > struct tsc2046_adc_priv {
> > struct spi_device *spi;
> > const struct tsc2046_adc_dcfg *dcfg;
> >
> > struct iio_trigger *trig;
> > struct hrtimer trig_timer;
> > - spinlock_t trig_lock;
> > - unsigned int trig_more_count;
> > + enum tsc2046_state state;
> > + spinlock_t state_lock;
> >
> > struct spi_transfer xfer;
> > struct spi_message msg;
> > @@ -411,21 +418,47 @@ static const struct iio_info tsc2046_adc_info = {
> > .update_scan_mode = tsc2046_adc_update_scan_mode,
> > };
> >
> > -static enum hrtimer_restart tsc2046_adc_trig_more(struct hrtimer *hrtimer)
> > +static enum hrtimer_restart tsc2046_adc_timer(struct hrtimer *hrtimer)
> > {
> > struct tsc2046_adc_priv *priv = container_of(hrtimer,
> > struct tsc2046_adc_priv,
> > trig_timer);
> > unsigned long flags;
> >
> > - spin_lock_irqsave(&priv->trig_lock, flags);
> > -
> > - disable_irq_nosync(priv->spi->irq);
> > -
> > - priv->trig_more_count++;
> > - iio_trigger_poll(priv->trig);
> > -
> > - spin_unlock_irqrestore(&priv->trig_lock, flags);
> > + spin_lock_irqsave(&priv->state_lock, flags);
> > + switch (priv->state) {
> > + case TSC2046_STATE_ENABLE_IRQ_POLL:
> > + /*
> > + * IRQ handler called iio_trigger_poll() to sample ADC.
> > + * Here we
> > + * - re-enable IRQs
> > + * - start hrtimer for timeout if no IRQ will occur
> > + */
> > + priv->state = TSC2046_STATE_POLL;
> > + enable_irq(priv->spi->irq);
>
> I comment on this below, but I'm not sure why you don't move the enable_irq()
> here out of this timer function and then have the first entry of the timer
> go directly to TSC2046_STATE_POLL after a longer initial wait.
Hm... yes. You are right.
> It's been a long time since I looked at this, so perhaps I'm missing the
> point. What you have here works as far as I can see, it just seems to push
> more than necessary into the state machine.
The IRQ line is a level shifter connected to one of channels muxed to the core
ADC. If we switch internal muxer to different channel, the IRQ line will
change the state.
So, we need a trigger which:
- do not triggers if we do ADC readings.
- keeps triggering as long as we have some state changes on the IRQ line
- trigger only with specific rate
- still triggers for some amount of time after last interrupt event was
detected. Current implementation is doing only one extra read.
I reworked it a bit, will send new patch soon.
> > + hrtimer_start(&priv->trig_timer,
> > + ns_to_ktime(priv->scan_interval_us *
> > + NSEC_PER_USEC),
> > + HRTIMER_MODE_REL_SOFT);
> > + break;
> > -
> > - spin_unlock_irqrestore(&priv->trig_lock, flags);
> > + tim = ns_to_ktime((priv->scan_interval_us - priv->time_per_scan_us) *
> > + NSEC_PER_USEC);
> > + hrtimer_start(&priv->trig_timer, tim, HRTIMER_MODE_REL_SOFT);
>
> This moves enabling the irq to the first instance of the timer - is that ever too late?
no, we should disable IRQ if we do readings anyway.
> > }
> >
> > static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
> > @@ -493,8 +506,8 @@ static int tsc2046_adc_set_trigger_state(struct iio_trigger *trig, bool enable)
> > if (enable) {
> > enable_irq(priv->spi->irq);
> > } else {
> > + hrtimer_cancel(&priv->trig_timer);
>
> So this will wait for the callback to finish. However, is there a chance
> of an interrupt just after this but before disable_irq that ends up
> starting the timer again?
Yes, you are right. I'll rework it.
Regards,
Oleksij
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
...
> > >
> > > -static enum hrtimer_restart tsc2046_adc_trig_more(struct hrtimer *hrtimer)
> > > +static enum hrtimer_restart tsc2046_adc_timer(struct hrtimer *hrtimer)
> > > {
> > > struct tsc2046_adc_priv *priv = container_of(hrtimer,
> > > struct tsc2046_adc_priv,
> > > trig_timer);
> > > unsigned long flags;
> > >
> > > - spin_lock_irqsave(&priv->trig_lock, flags);
> > > -
> > > - disable_irq_nosync(priv->spi->irq);
> > > -
> > > - priv->trig_more_count++;
> > > - iio_trigger_poll(priv->trig);
> > > -
> > > - spin_unlock_irqrestore(&priv->trig_lock, flags);
> > > + spin_lock_irqsave(&priv->state_lock, flags);
> > > + switch (priv->state) {
> > > + case TSC2046_STATE_ENABLE_IRQ_POLL:
> > > + /*
> > > + * IRQ handler called iio_trigger_poll() to sample ADC.
> > > + * Here we
> > > + * - re-enable IRQs
> > > + * - start hrtimer for timeout if no IRQ will occur
> > > + */
> > > + priv->state = TSC2046_STATE_POLL;
> > > + enable_irq(priv->spi->irq);
> >
> > I comment on this below, but I'm not sure why you don't move the enable_irq()
> > here out of this timer function and then have the first entry of the timer
> > go directly to TSC2046_STATE_POLL after a longer initial wait.
>
> Hm... yes. You are right.
>
> > It's been a long time since I looked at this, so perhaps I'm missing the
> > point. What you have here works as far as I can see, it just seems to push
> > more than necessary into the state machine.
>
> The IRQ line is a level shifter connected to one of channels muxed to the core
> ADC. If we switch internal muxer to different channel, the IRQ line will
> change the state.
>
> So, we need a trigger which:
> - do not triggers if we do ADC readings.
> - keeps triggering as long as we have some state changes on the IRQ line
> - trigger only with specific rate
> - still triggers for some amount of time after last interrupt event was
> detected. Current implementation is doing only one extra read.
Ah.. Good explanation, I get the point now :)
Jonathan