[PATCH] iio:st_magn: enable device after trigger

[PATCH] iio:st_magn: enable device after trigger

[Martin Kelly]

From: Martin Kelly <martin@martingkelly.com>

Currently, we enable the device before we enable the device trigger. At
high frequencies, this can cause interrupts that don't yet have a poll
function associated with them and are thus treated as spurious. At high
frequencies with level interrupts, this can even cause an interrupt storm
of repeated spurious interrupts (~100,000 on my Beagleboard with the
LSM9DS1 magnetometer). If these repeat too much, the interrupt will get
disabled and the device will stop functioning.

To prevent these problems, enable the device prior to enabling the device
trigger, and disable the divec prior to disabling the trigger. This means
there's no window of time during which the device creates interrupts but we
have no trigger to answer them.

Fixes: 90efe055629 ("iio: st_sensors: harden interrupt handling")
Signed-off-by: Martin Kelly <martin@martingkelly.com>
Tested-by: Denis Ciocca <denis.ciocca@st.com>
---
Note that, during testing of this change, Denis Ciocca noticed that when we fail
to disable the IIO buffer, we bail immediately and don't disable the sensor.
This commit does not fix that issue, but that should be fixed in a follow-up
commit. I will leave it to Denis, since he noticed the issue, but I'd be happy
to send a patch for it if he doesn't.

 drivers/iio/magnetometer/st_magn_buffer.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/iio/magnetometer/st_magn_buffer.c b/drivers/iio/magnetometer/st_magn_buffer.c
index 0a9e8fadfa9d..37ab30566464 100644
--- a/drivers/iio/magnetometer/st_magn_buffer.c
+++ b/drivers/iio/magnetometer/st_magn_buffer.c
@@ -30,11 +30,6 @@ int st_magn_trig_set_state(struct iio_trigger *trig, bool state)
 	return st_sensors_set_dataready_irq(indio_dev, state);
 }

-static int st_magn_buffer_preenable(struct iio_dev *indio_dev)
-{
-	return st_sensors_set_enable(indio_dev, true);
-}
-
 static int st_magn_buffer_postenable(struct iio_dev *indio_dev)
 {
 	int err;
@@ -50,7 +45,7 @@ static int st_magn_buffer_postenable(struct iio_dev *indio_dev)
 	if (err < 0)
 		goto st_magn_buffer_postenable_error;

-	return err;
+	return st_sensors_set_enable(indio_dev, true);

 st_magn_buffer_postenable_error:
 	kfree(mdata->buffer_data);
@@ -63,11 +58,11 @@ static int st_magn_buffer_predisable(struct iio_dev *indio_dev)
 	int err;
 	struct st_sensor_data *mdata = iio_priv(indio_dev);

-	err = iio_triggered_buffer_predisable(indio_dev);
+	err = st_sensors_set_enable(indio_dev, false);
 	if (err < 0)
 		goto st_magn_buffer_predisable_error;

-	err = st_sensors_set_enable(indio_dev, false);
+	err = iio_triggered_buffer_predisable(indio_dev);

 st_magn_buffer_predisable_error:
 	kfree(mdata->buffer_data);
@@ -75,7 +70,6 @@ static int st_magn_buffer_predisable(struct iio_dev *indio_dev)
 }

 static const struct iio_buffer_setup_ops st_magn_buffer_setup_ops = {
-	.preenable = &st_magn_buffer_preenable,
 	.postenable = &st_magn_buffer_postenable,
 	.predisable = &st_magn_buffer_predisable,
 };
--
2.11.0

Re: [PATCH] iio:st_magn: enable device after trigger

[Jonathan Cameron]

On Sun, 28 Oct 2018 20:18:53 -0700
Martin Kelly <martin@martingkelly.com> wrote:

> From: Martin Kelly <martin@martingkelly.com>
> 
> Currently, we enable the device before we enable the device trigger. At
> high frequencies, this can cause interrupts that don't yet have a poll
> function associated with them and are thus treated as spurious. At high
> frequencies with level interrupts, this can even cause an interrupt storm
> of repeated spurious interrupts (~100,000 on my Beagleboard with the
> LSM9DS1 magnetometer). If these repeat too much, the interrupt will get
> disabled and the device will stop functioning.
> 
> To prevent these problems, enable the device prior to enabling the device
> trigger, and disable the divec prior to disabling the trigger. This means
> there's no window of time during which the device creates interrupts but we
> have no trigger to answer them.
> 
> Fixes: 90efe055629 ("iio: st_sensors: harden interrupt handling")
> Signed-off-by: Martin Kelly <martin@martingkelly.com>
> Tested-by: Denis Ciocca <denis.ciocca@st.com>
Added Fix to the title to make that obvious.

Applied to the fixes-togreg branch of iio.git and marked for stable
inclusion.

Thanks,

Jonathan

> ---
> Note that, during testing of this change, Denis Ciocca noticed that when we fail
> to disable the IIO buffer, we bail immediately and don't disable the sensor.
> This commit does not fix that issue, but that should be fixed in a follow-up
> commit. I will leave it to Denis, since he noticed the issue, but I'd be happy
> to send a patch for it if he doesn't.
> 
>  drivers/iio/magnetometer/st_magn_buffer.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iio/magnetometer/st_magn_buffer.c b/drivers/iio/magnetometer/st_magn_buffer.c
> index 0a9e8fadfa9d..37ab30566464 100644
> --- a/drivers/iio/magnetometer/st_magn_buffer.c
> +++ b/drivers/iio/magnetometer/st_magn_buffer.c
> @@ -30,11 +30,6 @@ int st_magn_trig_set_state(struct iio_trigger *trig, bool state)
>  	return st_sensors_set_dataready_irq(indio_dev, state);
>  }
> 
> -static int st_magn_buffer_preenable(struct iio_dev *indio_dev)
> -{
> -	return st_sensors_set_enable(indio_dev, true);
> -}
> -
>  static int st_magn_buffer_postenable(struct iio_dev *indio_dev)
>  {
>  	int err;
> @@ -50,7 +45,7 @@ static int st_magn_buffer_postenable(struct iio_dev *indio_dev)
>  	if (err < 0)
>  		goto st_magn_buffer_postenable_error;
> 
> -	return err;
> +	return st_sensors_set_enable(indio_dev, true);
> 
>  st_magn_buffer_postenable_error:
>  	kfree(mdata->buffer_data);
> @@ -63,11 +58,11 @@ static int st_magn_buffer_predisable(struct iio_dev *indio_dev)
>  	int err;
>  	struct st_sensor_data *mdata = iio_priv(indio_dev);
> 
> -	err = iio_triggered_buffer_predisable(indio_dev);
> +	err = st_sensors_set_enable(indio_dev, false);
>  	if (err < 0)
>  		goto st_magn_buffer_predisable_error;
> 
> -	err = st_sensors_set_enable(indio_dev, false);
> +	err = iio_triggered_buffer_predisable(indio_dev);
> 
>  st_magn_buffer_predisable_error:
>  	kfree(mdata->buffer_data);
> @@ -75,7 +70,6 @@ static int st_magn_buffer_predisable(struct iio_dev *indio_dev)
>  }
> 
>  static const struct iio_buffer_setup_ops st_magn_buffer_setup_ops = {
> -	.preenable = &st_magn_buffer_preenable,
>  	.postenable = &st_magn_buffer_postenable,
>  	.predisable = &st_magn_buffer_predisable,
>  };
> --
> 2.11.0
>