[PATCH 1/2 v6] iio: st_sensors: switch to a threaded interrupt

[PATCH 1/2 v6] iio: st_sensors: switch to a threaded interrupt

[Linus Walleij]

commit 98ad8b41f58dff6b30713d7f09ae3834b8df7ded
("iio: st_sensors: verify interrupt event to status") caused
a regression when reading ST sensors from a HRTimer trigger
rather than the intrinsic interrupts: the HRTimer may
trigger faster than the sensor provides new values, and
as the check against new values available as a cause of
the interrupt trigger was done in the poll function,
this would bail out of the HRTimer interrupt with
IRQ_NONE.

So clearly we need to only check the new values available
from the proper interrupt handler and not from the poll
function, which should rather just read the raw values
from the registers, put them into the buffer and be happy.

To achieve this: switch the ST Sensors over to using a true
threaded interrupt handler.

In the interrupt thread, check if new values are available,
else yield to the (potential) next device on the same
interrupt line to check the registers. If the interrupt
was ours, proceed to poll the values.

Instead of relying on iio_trigger_generic_data_rdy_poll() as
a top half to wake up the thread that polls the sensor for
new data, have the thread call iio_trigger_poll_chained()
after determining that is is the proper source of the
interrupt. This is modelled on drivers/iio/accel/mma8452.c
which is already using a properly threaded interrupt handler.

In order to get the same precision in timestamps as
previously, where samples would be timestamped in the
poll function pf->timestamp when calling
iio_trigger_generic_data_rdy_poll() we introduce a
local timestamp in the sensor data, set it in the top half
(fastpath) of the interrupt handler and provide that to the
core when calling iio_push_to_buffers_with_timestamp().

Additionally: if the active scanmask is not set for the
sensor no IRQs should be enabled and we need to bail out
with IRQ_NONE. This can happen if spurious IRQs fire when
installing the threaded interrupt handler.

Tested with hard interrupt triggers on LIS331DL, then also
tested with hrtimers on the same sensor by creating a 75Hz
HRTimer and using it to poll the sensor.

Cc: Giuseppe Barba <giuseppe.barba@st.com>
Cc: Denis Ciocca <denis.ciocca@st.com>
Reported-by: Crestez Dan Leonard <cdleonard@gmail.com>
Tested-by: Crestez Dan Leonard <cdleonard@gmail.com>
Fixes: 97865fe41322 ("iio: st_sensors: verify interrupt event to status")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v5->v6:
- Set the triggered buffer top half IRQ handler to NULL in all
  subdrivers (accelerometer, gyro, magnetometer, pressure) as
  we now use the iio_trigger_poll_chained() call.
- Add st_sensors_validate_device() to the intrinsic triggers
  and set as .validate_deice() for all subdrivers. Its purpose
  is to check that the trigger is indeed provided by this
  device before we use it.
- NOTE: this patch is a regression fix and can be applied
  without 2/2.
ChangeLog v4->v5:
- Move the setting of hw_irq_enabled to before the register
  write to enable interrupts so we avoid a race where this
  variable could be read in its previous state.
ChangeLog v3->v4:
- v3 would not timestamp properly when using a HRTimer to read
  values from the sensors. This is now fixed.
- Add a flag to the sensor data indicating whether the hardware
  interrupt trigger is in use. If this is the case, we use that
  timestamp. If the hardware trigger is not in use, we just let
  the poll function read the current time before proceeding to
  grab the values from the sensor.
- Move interrupt top/bottom halves to st_sensors_trigger.c so the
  interrupt code is kept together and easier to understand in
  context.
ChangeLog v2->v3:
- v2 was a total disaster, as iio_trigger_generic_data_rdy_poll()
  would just call the old bottom half and return IRQ_HANDLED.
  handle the timestamp locally in the sensor data and restore
  the usage of the local interrupt thread.
- I think it works now.
ChangeLog v1->v2:
- v1 was missing timestamps since nothing ever stamped them.
  Restore the timestamps by simply using
  iio_trigger_generic_data_rdy_poll()
  as the top half of the threaded interrupt handler.
---
 drivers/iio/accel/st_accel_buffer.c                |  2 +-
 drivers/iio/accel/st_accel_core.c                  |  1 +
 drivers/iio/common/st_sensors/st_sensors_buffer.c  | 25 ++-----
 drivers/iio/common/st_sensors/st_sensors_core.c    |  3 +
 drivers/iio/common/st_sensors/st_sensors_trigger.c | 80 +++++++++++++++++++++-
 drivers/iio/gyro/st_gyro_buffer.c                  |  2 +-
 drivers/iio/gyro/st_gyro_core.c                    |  1 +
 drivers/iio/magnetometer/st_magn_buffer.c          |  2 +-
 drivers/iio/magnetometer/st_magn_core.c            |  1 +
 drivers/iio/pressure/st_pressure_buffer.c          |  2 +-
 drivers/iio/pressure/st_pressure_core.c            |  1 +
 include/linux/iio/common/st_sensors.h              |  9 ++-
 12 files changed, 103 insertions(+), 26 deletions(-)

diff --git a/drivers/iio/accel/st_accel_buffer.c b/drivers/iio/accel/st_accel_buffer.c
index a1e642ee13d6..7fddc137e91e 100644
--- a/drivers/iio/accel/st_accel_buffer.c
+++ b/drivers/iio/accel/st_accel_buffer.c
@@ -91,7 +91,7 @@ static const struct iio_buffer_setup_ops st_accel_buffer_setup_ops = {
 
 int st_accel_allocate_ring(struct iio_dev *indio_dev)
 {
-	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
+	return iio_triggered_buffer_setup(indio_dev, NULL,
 		&st_sensors_trigger_handler, &st_accel_buffer_setup_ops);
 }
 
diff --git a/drivers/iio/accel/st_accel_core.c b/drivers/iio/accel/st_accel_core.c
index f06f4329db5b..1d9291116556 100644
--- a/drivers/iio/accel/st_accel_core.c
+++ b/drivers/iio/accel/st_accel_core.c
@@ -649,6 +649,7 @@ static const struct iio_info accel_info = {
 static const struct iio_trigger_ops st_accel_trigger_ops = {
 	.owner = THIS_MODULE,
 	.set_trigger_state = ST_ACCEL_TRIGGER_SET_STATE,
+	.validate_device = st_sensors_validate_device,
 };
 #define ST_ACCEL_TRIGGER_OPS (&st_accel_trigger_ops)
 #else
diff --git a/drivers/iio/common/st_sensors/st_sensors_buffer.c b/drivers/iio/common/st_sensors/st_sensors_buffer.c
index c55898543a47..f1693dbebb8a 100644
--- a/drivers/iio/common/st_sensors/st_sensors_buffer.c
+++ b/drivers/iio/common/st_sensors/st_sensors_buffer.c
@@ -57,31 +57,20 @@ irqreturn_t st_sensors_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct st_sensor_data *sdata = iio_priv(indio_dev);
+	s64 timestamp;
 
-	/* If we have a status register, check if this IRQ came from us */
-	if (sdata->sensor_settings->drdy_irq.addr_stat_drdy) {
-		u8 status;
-
-		len = sdata->tf->read_byte(&sdata->tb, sdata->dev,
-			   sdata->sensor_settings->drdy_irq.addr_stat_drdy,
-			   &status);
-		if (len < 0)
-			dev_err(sdata->dev, "could not read channel status\n");
-
-		/*
-		 * If this was not caused by any channels on this sensor,
-		 * return IRQ_NONE
-		 */
-		if (!(status & (u8)indio_dev->active_scan_mask[0]))
-			return IRQ_NONE;
-	}
+	/* If we do timetamping here, do it before reading the values */
+	if (sdata->hw_irq_trigger)
+		timestamp = sdata->hw_timestamp;
+	else
+		timestamp = iio_get_time_ns();
 
 	len = st_sensors_get_buffer_element(indio_dev, sdata->buffer_data);
 	if (len < 0)
 		goto st_sensors_get_buffer_element_error;
 
 	iio_push_to_buffers_with_timestamp(indio_dev, sdata->buffer_data,
-		pf->timestamp);
+					   timestamp);
 
 st_sensors_get_buffer_element_error:
 	iio_trigger_notify_done(indio_dev->trig);
diff --git a/drivers/iio/common/st_sensors/st_sensors_core.c b/drivers/iio/common/st_sensors/st_sensors_core.c
index dffe00692169..928ee68fcc5f 100644
--- a/drivers/iio/common/st_sensors/st_sensors_core.c
+++ b/drivers/iio/common/st_sensors/st_sensors_core.c
@@ -424,6 +424,9 @@ int st_sensors_set_dataready_irq(struct iio_dev *indio_dev, bool enable)
 	else
 		drdy_mask = sdata->sensor_settings->drdy_irq.mask_int2;
 
+	/* Flag to the poll function that the hardware trigger is in use */
+	sdata->hw_irq_trigger = enable;
+
 	/* Enable/Disable the interrupt generator for data ready. */
 	err = st_sensors_write_data_with_mask(indio_dev,
 					sdata->sensor_settings->drdy_irq.addr,
diff --git a/drivers/iio/common/st_sensors/st_sensors_trigger.c b/drivers/iio/common/st_sensors/st_sensors_trigger.c
index da72279fcf99..98bd5b3b868f 100644
--- a/drivers/iio/common/st_sensors/st_sensors_trigger.c
+++ b/drivers/iio/common/st_sensors/st_sensors_trigger.c
@@ -17,6 +17,65 @@
 #include <linux/iio/common/st_sensors.h>
 #include "st_sensors_core.h"
 
+/**
+ * st_sensors_irq_handler() - top half of the IRQ-based triggers
+ * @irq: irq number
+ * @p: private handler data
+ */
+irqreturn_t st_sensors_irq_handler(int irq, void *p)
+{
+	struct iio_trigger *trig = p;
+	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
+	struct st_sensor_data *sdata = iio_priv(indio_dev);
+
+	/* Get the time stamp as close in time as possible */
+	sdata->hw_timestamp = iio_get_time_ns();
+	return IRQ_WAKE_THREAD;
+}
+
+/**
+ * st_sensors_irq_thread() - bottom half of the IRQ-based triggers
+ * @irq: irq number
+ * @p: private handler data
+ */
+irqreturn_t st_sensors_irq_thread(int irq, void *p)
+{
+	struct iio_trigger *trig = p;
+	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
+	struct st_sensor_data *sdata = iio_priv(indio_dev);
+	int ret;
+
+	/*
+	 * If this trigger is backed by a hardware interrupt and we have a
+	 * status register, check if this IRQ came from us
+	 */
+	if (sdata->sensor_settings->drdy_irq.addr_stat_drdy) {
+		u8 status;
+
+		ret = sdata->tf->read_byte(&sdata->tb, sdata->dev,
+			   sdata->sensor_settings->drdy_irq.addr_stat_drdy,
+			   &status);
+		if (ret < 0) {
+			dev_err(sdata->dev, "could not read channel status\n");
+			goto out_poll;
+		}
+
+		/*
+		 * If this was not caused by any channels on this sensor,
+		 * return IRQ_NONE
+		 */
+		if (!indio_dev->active_scan_mask)
+			return IRQ_NONE;
+		if (!(status & (u8)indio_dev->active_scan_mask[0]))
+			return IRQ_NONE;
+	}
+
+out_poll:
+	/* It's our IRQ: proceed to handle the register polling */
+	iio_trigger_poll_chained(p);
+	return IRQ_HANDLED;
+}
+
 int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 				const struct iio_trigger_ops *trigger_ops)
 {
@@ -77,9 +136,12 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 	    sdata->sensor_settings->drdy_irq.addr_stat_drdy)
 		irq_trig |= IRQF_SHARED;
 
-	err = request_threaded_irq(irq,
-			iio_trigger_generic_data_rdy_poll,
-			NULL,
+	/* Let's create an interrupt thread masking the hard IRQ here */
+	irq_trig |= IRQF_ONESHOT;
+
+	err = request_threaded_irq(sdata->get_irq_data_ready(indio_dev),
+			st_sensors_irq_handler,
+			st_sensors_irq_thread,
 			irq_trig,
 			sdata->trig->name,
 			sdata->trig);
@@ -119,6 +181,18 @@ void st_sensors_deallocate_trigger(struct iio_dev *indio_dev)
 }
 EXPORT_SYMBOL(st_sensors_deallocate_trigger);
 
+int st_sensors_validate_device(struct iio_trigger *trig,
+			       struct iio_dev *indio_dev)
+{
+	struct iio_dev *indio = iio_trigger_get_drvdata(trig);
+
+	if (indio != indio_dev)
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL(st_sensors_validate_device);
+
 MODULE_AUTHOR("Denis Ciocca <denis.ciocca@st.com>");
 MODULE_DESCRIPTION("STMicroelectronics ST-sensors trigger");
 MODULE_LICENSE("GPL v2");
diff --git a/drivers/iio/gyro/st_gyro_buffer.c b/drivers/iio/gyro/st_gyro_buffer.c
index d67b17b6a7aa..a5377044e42f 100644
--- a/drivers/iio/gyro/st_gyro_buffer.c
+++ b/drivers/iio/gyro/st_gyro_buffer.c
@@ -91,7 +91,7 @@ static const struct iio_buffer_setup_ops st_gyro_buffer_setup_ops = {
 
 int st_gyro_allocate_ring(struct iio_dev *indio_dev)
 {
-	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
+	return iio_triggered_buffer_setup(indio_dev, NULL,
 		&st_sensors_trigger_handler, &st_gyro_buffer_setup_ops);
 }
 
diff --git a/drivers/iio/gyro/st_gyro_core.c b/drivers/iio/gyro/st_gyro_core.c
index be9057e89dc3..242a3e3c88e4 100644
--- a/drivers/iio/gyro/st_gyro_core.c
+++ b/drivers/iio/gyro/st_gyro_core.c
@@ -408,6 +408,7 @@ static const struct iio_info gyro_info = {
 static const struct iio_trigger_ops st_gyro_trigger_ops = {
 	.owner = THIS_MODULE,
 	.set_trigger_state = ST_GYRO_TRIGGER_SET_STATE,
+	.validate_device = st_sensors_validate_device,
 };
 #define ST_GYRO_TRIGGER_OPS (&st_gyro_trigger_ops)
 #else
diff --git a/drivers/iio/magnetometer/st_magn_buffer.c b/drivers/iio/magnetometer/st_magn_buffer.c
index ecd3bd0a9769..0a9e8fadfa9d 100644
--- a/drivers/iio/magnetometer/st_magn_buffer.c
+++ b/drivers/iio/magnetometer/st_magn_buffer.c
@@ -82,7 +82,7 @@ static const struct iio_buffer_setup_ops st_magn_buffer_setup_ops = {
 
 int st_magn_allocate_ring(struct iio_dev *indio_dev)
 {
-	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
+	return iio_triggered_buffer_setup(indio_dev, NULL,
 		&st_sensors_trigger_handler, &st_magn_buffer_setup_ops);
 }
 
diff --git a/drivers/iio/magnetometer/st_magn_core.c b/drivers/iio/magnetometer/st_magn_core.c
index 62036d2a9956..8250fc322c56 100644
--- a/drivers/iio/magnetometer/st_magn_core.c
+++ b/drivers/iio/magnetometer/st_magn_core.c
@@ -572,6 +572,7 @@ static const struct iio_info magn_info = {
 static const struct iio_trigger_ops st_magn_trigger_ops = {
 	.owner = THIS_MODULE,
 	.set_trigger_state = ST_MAGN_TRIGGER_SET_STATE,
+	.validate_device = st_sensors_validate_device,
 };
 #define ST_MAGN_TRIGGER_OPS (&st_magn_trigger_ops)
 #else
diff --git a/drivers/iio/pressure/st_pressure_buffer.c b/drivers/iio/pressure/st_pressure_buffer.c
index 2ff53f222352..99468d0a64e7 100644
--- a/drivers/iio/pressure/st_pressure_buffer.c
+++ b/drivers/iio/pressure/st_pressure_buffer.c
@@ -82,7 +82,7 @@ static const struct iio_buffer_setup_ops st_press_buffer_setup_ops = {
 
 int st_press_allocate_ring(struct iio_dev *indio_dev)
 {
-	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
+	return iio_triggered_buffer_setup(indio_dev, NULL,
 		&st_sensors_trigger_handler, &st_press_buffer_setup_ops);
 }
 
diff --git a/drivers/iio/pressure/st_pressure_core.c b/drivers/iio/pressure/st_pressure_core.c
index 9e9b72a8f18f..b48285739246 100644
--- a/drivers/iio/pressure/st_pressure_core.c
+++ b/drivers/iio/pressure/st_pressure_core.c
@@ -425,6 +425,7 @@ static const struct iio_info press_info = {
 static const struct iio_trigger_ops st_press_trigger_ops = {
 	.owner = THIS_MODULE,
 	.set_trigger_state = ST_PRESS_TRIGGER_SET_STATE,
+	.validate_device = st_sensors_validate_device,
 };
 #define ST_PRESS_TRIGGER_OPS (&st_press_trigger_ops)
 #else
diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
index d029ffac0d69..99403b19092f 100644
--- a/include/linux/iio/common/st_sensors.h
+++ b/include/linux/iio/common/st_sensors.h
@@ -223,6 +223,8 @@ struct st_sensor_settings {
  * @get_irq_data_ready: Function to get the IRQ used for data ready signal.
  * @tf: Transfer function structure used by I/O operations.
  * @tb: Transfer buffers and mutex used by I/O operations.
+ * @hw_irq_trigger: if we're using the hardware interrupt on the sensor.
+ * @hw_timestamp: Latest timestamp from the interrupt handler, when in use.
  */
 struct st_sensor_data {
 	struct device *dev;
@@ -247,6 +249,9 @@ struct st_sensor_data {
 
 	const struct st_sensor_transfer_function *tf;
 	struct st_sensor_transfer_buffer tb;
+
+	bool hw_irq_trigger;
+	s64 hw_timestamp;
 };
 
 #ifdef CONFIG_IIO_BUFFER
@@ -260,7 +265,8 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 				const struct iio_trigger_ops *trigger_ops);
 
 void st_sensors_deallocate_trigger(struct iio_dev *indio_dev);
-
+int st_sensors_validate_device(struct iio_trigger *trig,
+			       struct iio_dev *indio_dev);
 #else
 static inline int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 				const struct iio_trigger_ops *trigger_ops)
@@ -271,6 +277,7 @@ static inline void st_sensors_deallocate_trigger(struct iio_dev *indio_dev)
 {
 	return;
 }
+#define st_sensors_validate_device NULL
 #endif
 
 int st_sensors_init_sensor(struct iio_dev *indio_dev,
-- 
2.4.11

[PATCH 2/2 v6] iio: st_sensors: read surplus samples in trigger

[Linus Walleij]

Leonard Crestez observed the following phenomenon: when using
hard interrupt triggers (the DRDY line coming out of an ST
sensor) sometimes a new value would arrive while reading the
previous value, due to latencies in the system.

As the interrupts from the ST sensors are a pulse, intended
to be read by an edge-triggered interrupt line (such as a
GPIO) one edge (transition from low-to-high or high-to-low)
will be missed while processing the current values.

If this happens, the state machine that triggers interrupts on
the DRDY line will lock waiting for the current value to be
read out and not fire any more interrupts. That means that
when we exit the interrupt handler, even though new values are
available from the sensor, no new interrupt will be triggered.

To counter this, do two things:

- Remove IRQF_ONESHOT so that the interrupt line is not
  masked while running the thread part of the interrupt.
  This way we will never miss an interrupt.

- Introduce a loop that polls the data ready
  registers repeatedly until no new samples are available,
  then exits the interrupt handler. This way we know no new
  values are available when the interrupt handler exits and
  new interrupts will be triggered when data arrives.
  Take some extra care to update the timestamp for the poll
  function if this happens. The timestamp will not be 100%
  perfect, but it will at least be closer to the actual
  events.

Usually the extra poll loop will handle the new samples,
but once in a blue moon, we get a new IRQ while exiting
the loop, before returning from the thread IRQ bottom half
with IRQ_HANDLED. On these rare occasions, the removal of
IRQF_ONESHOT means the interrupt will immediately fire
again.

Tested successfully on the LIS331DL by setting sampling
frequency to 400Hz and stressing the system: extra reads in
the threaded interrupt handler occurs.

Cc: Giuseppe Barba <giuseppe.barba@st.com>
Cc: Denis Ciocca <denis.ciocca@st.com>
Cc: Crestez Dan Leonard <cdleonard@gmail.com>
Reported-by: Crestez Dan Leonard <cdleonard@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v5->v6:
- Add a loop counter to the threaded value poll function: let's
  just loop here for at maximum 10 loops before we exit and
  let the thread re-trigger if more interrupts arrived.
ChangeLog v4->v5:
- Remove the IRQF_ONESHOT flag from the interrupt: this makes
  it possible to trigger the top half of the interrupt even
  though the bottom half is processing an earlier interrupt.
  This makes it possible to gracefully handle interrupts that
  come in during sensor reading.
- Add better descriptive comments.
ChangeLog v3->v4:
- Include this patch with the threaded interrupt fix patch.
  Adapte the same patch numbering system.

If this works I suggest it be applied to mainline as a fix on
top of the threading patch version 3, so we handle this annoying
lockup bug.
---
 drivers/iio/common/st_sensors/st_sensors_buffer.c  |  7 +-
 drivers/iio/common/st_sensors/st_sensors_trigger.c | 79 +++++++++++++++-------
 2 files changed, 59 insertions(+), 27 deletions(-)

diff --git a/drivers/iio/common/st_sensors/st_sensors_buffer.c b/drivers/iio/common/st_sensors/st_sensors_buffer.c
index f1693dbebb8a..f6873919f188 100644
--- a/drivers/iio/common/st_sensors/st_sensors_buffer.c
+++ b/drivers/iio/common/st_sensors/st_sensors_buffer.c
@@ -59,7 +59,12 @@ irqreturn_t st_sensors_trigger_handler(int irq, void *p)
 	struct st_sensor_data *sdata = iio_priv(indio_dev);
 	s64 timestamp;
 
-	/* If we do timetamping here, do it before reading the values */
+	/*
+	 * If we do timetamping here, do it before reading the values, because
+	 * once we've read the values, new interrupts can occur (when using
+	 * the hardware trigger) and the hw_timestamp may get updated.
+	 * By storing it in a local variable first, we are safe.
+	 */
 	if (sdata->hw_irq_trigger)
 		timestamp = sdata->hw_timestamp;
 	else
diff --git a/drivers/iio/common/st_sensors/st_sensors_trigger.c b/drivers/iio/common/st_sensors/st_sensors_trigger.c
index 98bd5b3b868f..3e260d6ecda8 100644
--- a/drivers/iio/common/st_sensors/st_sensors_trigger.c
+++ b/drivers/iio/common/st_sensors/st_sensors_trigger.c
@@ -18,6 +18,42 @@
 #include "st_sensors_core.h"
 
 /**
+ * st_sensors_new_samples_available() - check if more samples came in
+ * returns:
+ * 0 - no new samples available
+ * 1 - new samples available
+ * negative - error or unknown
+ */
+static int st_sensors_new_samples_available(struct iio_dev *indio_dev,
+					    struct st_sensor_data *sdata)
+{
+	u8 status;
+	int ret;
+
+	/* How would I know if I can't check it? */
+	if (!sdata->sensor_settings->drdy_irq.addr_stat_drdy)
+		return -EINVAL;
+
+	/* No scan mask, no interrupt */
+	if (!indio_dev->active_scan_mask)
+		return 0;
+
+	ret = sdata->tf->read_byte(&sdata->tb, sdata->dev,
+			sdata->sensor_settings->drdy_irq.addr_stat_drdy,
+			&status);
+	if (ret < 0) {
+		dev_err(sdata->dev,
+			"error checking samples available\n");
+		return ret;
+	}
+
+	if (status & (u8)indio_dev->active_scan_mask[0])
+		return 1;
+
+	return 0;
+}
+
+/**
  * st_sensors_irq_handler() - top half of the IRQ-based triggers
  * @irq: irq number
  * @p: private handler data
@@ -43,36 +79,30 @@ irqreturn_t st_sensors_irq_thread(int irq, void *p)
 	struct iio_trigger *trig = p;
 	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
 	struct st_sensor_data *sdata = iio_priv(indio_dev);
-	int ret;
+	/* Loop for new values maximum 10 times */
+	int loops = 10;
 
 	/*
 	 * If this trigger is backed by a hardware interrupt and we have a
-	 * status register, check if this IRQ came from us
+	 * status register, check if this IRQ came from us. Notice that
+	 * we will process also if st_sensors_new_samples_available()
+	 * returns negative: if we can't check status, then poll
+	 * unconditionally.
 	 */
-	if (sdata->sensor_settings->drdy_irq.addr_stat_drdy) {
-		u8 status;
-
-		ret = sdata->tf->read_byte(&sdata->tb, sdata->dev,
-			   sdata->sensor_settings->drdy_irq.addr_stat_drdy,
-			   &status);
-		if (ret < 0) {
-			dev_err(sdata->dev, "could not read channel status\n");
-			goto out_poll;
-		}
+	if (st_sensors_new_samples_available(indio_dev, sdata)) {
+		iio_trigger_poll_chained(p);
+	} else {
+		dev_dbg(sdata->dev, "spurious IRQ\n");
+		return IRQ_NONE;
+	}
 
-		/*
-		 * If this was not caused by any channels on this sensor,
-		 * return IRQ_NONE
-		 */
-		if (!indio_dev->active_scan_mask)
-			return IRQ_NONE;
-		if (!(status & (u8)indio_dev->active_scan_mask[0]))
-			return IRQ_NONE;
+	/* If new samples arrived while processing the IRQ, poll again. */
+	while (loops-- && st_sensors_new_samples_available(indio_dev, sdata)) {
+		dev_dbg(sdata->dev, "more samples came in during polling\n");
+		sdata->hw_timestamp = iio_get_time_ns();
+		iio_trigger_poll_chained(p);
 	}
 
-out_poll:
-	/* It's our IRQ: proceed to handle the register polling */
-	iio_trigger_poll_chained(p);
 	return IRQ_HANDLED;
 }
 
@@ -136,9 +166,6 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
 	    sdata->sensor_settings->drdy_irq.addr_stat_drdy)
 		irq_trig |= IRQF_SHARED;
 
-	/* Let's create an interrupt thread masking the hard IRQ here */
-	irq_trig |= IRQF_ONESHOT;
-
 	err = request_threaded_irq(sdata->get_irq_data_ready(indio_dev),
 			st_sensors_irq_handler,
 			st_sensors_irq_thread,
-- 
2.4.11

Re: [PATCH 2/2 v6] iio: st_sensors: read surplus samples in trigger

[Crestez Dan Leonard]

On 05/10/2016 12:00 PM, Linus Walleij wrote:
> Leonard Crestez observed the following phenomenon: when using
> hard interrupt triggers (the DRDY line coming out of an ST
> sensor) sometimes a new value would arrive while reading the
> previous value, due to latencies in the system.
> 
> As the interrupts from the ST sensors are a pulse, intended
> to be read by an edge-triggered interrupt line (such as a
> GPIO) one edge (transition from low-to-high or high-to-low)
> will be missed while processing the current values.
> 
> If this happens, the state machine that triggers interrupts on
> the DRDY line will lock waiting for the current value to be
> read out and not fire any more interrupts. That means that
> when we exit the interrupt handler, even though new values are
> available from the sensor, no new interrupt will be triggered.
> 
> ChangeLog v5->v6:
> - Add a loop counter to the threaded value poll function: let's
>   just loop here for at maximum 10 loops before we exit and
>   let the thread re-trigger if more interrupts arrived.

This only serves to hide the problem. Version 5 seems preferable. Or
even just adding msleep(10) in that infinite loop.

-- 
Regards,
Leonard

Re: [PATCH 2/2 v6] iio: st_sensors: read surplus samples in trigger

[Linus Walleij]

On Tue, May 10, 2016 at 6:40 PM, Crestez Dan Leonard
<leonard.crestez@intel.com> wrote:
> [Me]
>> ChangeLog v5->v6:
>> - Add a loop counter to the threaded value poll function: let's
>>   just loop here for at maximum 10 loops before we exit and
>>   let the thread re-trigger if more interrupts arrived.
>
> This only serves to hide the problem.

Not really. The system can preempt after exiting the thread but
before processing the next set of samples.

> Version 5 seems preferable. Or
> even just adding msleep(10) in that infinite loop.

That provides a preemption point I guess but usleep_range()
is usually preferrable for such cases. 10ms is way to long
time to wait, because the max sample frequency will be
1/10ms = 100Hz and some ST sensors I have support
1kHz updates even. The usleep range would need to be
very short.

Yours,
Linus Walleij

Re: [PATCH 1/2 v6] iio: st_sensors: switch to a threaded interrupt

[Crestez Dan Leonard]

On 05/10/2016 12:00 PM, Linus Walleij wrote:
> commit 98ad8b41f58dff6b30713d7f09ae3834b8df7ded
> ("iio: st_sensors: verify interrupt event to status") caused
> a regression when reading ST sensors from a HRTimer trigger
> rather than the intrinsic interrupts: the HRTimer may
> trigger faster than the sensor provides new values, and
> as the check against new values available as a cause of
> the interrupt trigger was done in the poll function,
> this would bail out of the HRTimer interrupt with
> IRQ_NONE.
> 
> So clearly we need to only check the new values available
> from the proper interrupt handler and not from the poll
> function, which should rather just read the raw values
> from the registers, put them into the buffer and be happy.
> 
> To achieve this: switch the ST Sensors over to using a true
> threaded interrupt handler.
> 
> In the interrupt thread, check if new values are available,
> else yield to the (potential) next device on the same
> interrupt line to check the registers. If the interrupt
> was ours, proceed to poll the values.
> 
> Instead of relying on iio_trigger_generic_data_rdy_poll() as
> a top half to wake up the thread that polls the sensor for
> new data, have the thread call iio_trigger_poll_chained()
> after determining that is is the proper source of the
> interrupt. This is modelled on drivers/iio/accel/mma8452.c
> which is already using a properly threaded interrupt handler.
> 
> In order to get the same precision in timestamps as
> previously, where samples would be timestamped in the
> poll function pf->timestamp when calling
> iio_trigger_generic_data_rdy_poll() we introduce a
> local timestamp in the sensor data, set it in the top half
> (fastpath) of the interrupt handler and provide that to the
> core when calling iio_push_to_buffers_with_timestamp().
> 
> Additionally: if the active scanmask is not set for the
> sensor no IRQs should be enabled and we need to bail out
> with IRQ_NONE. This can happen if spurious IRQs fire when
> installing the threaded interrupt handler.
> 
> Tested with hard interrupt triggers on LIS331DL, then also
> tested with hrtimers on the same sensor by creating a 75Hz
> HRTimer and using it to poll the sensor.
> 
> Cc: Giuseppe Barba <giuseppe.barba@st.com>
> Cc: Denis Ciocca <denis.ciocca@st.com>
> Reported-by: Crestez Dan Leonard <cdleonard@gmail.com>
> Tested-by: Crestez Dan Leonard <cdleonard@gmail.com>
> Fixes: 97865fe41322 ("iio: st_sensors: verify interrupt event to status")
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Patch 2 is questionable but this patch works great and fixes a distinct
issue. It should be applied separately.

-- 
Regards,
Leonard

Re: [PATCH 1/2 v6] iio: st_sensors: switch to a threaded interrupt

[Jonathan Cameron]

On 10/05/16 10:00, Linus Walleij wrote:
> commit 98ad8b41f58dff6b30713d7f09ae3834b8df7ded
> ("iio: st_sensors: verify interrupt event to status") caused
> a regression when reading ST sensors from a HRTimer trigger
> rather than the intrinsic interrupts: the HRTimer may
> trigger faster than the sensor provides new values, and
> as the check against new values available as a cause of
> the interrupt trigger was done in the poll function,
> this would bail out of the HRTimer interrupt with
> IRQ_NONE.
> 
> So clearly we need to only check the new values available
> from the proper interrupt handler and not from the poll
> function, which should rather just read the raw values
> from the registers, put them into the buffer and be happy.
> 
> To achieve this: switch the ST Sensors over to using a true
> threaded interrupt handler.
> 
> In the interrupt thread, check if new values are available,
> else yield to the (potential) next device on the same
> interrupt line to check the registers. If the interrupt
> was ours, proceed to poll the values.
> 
> Instead of relying on iio_trigger_generic_data_rdy_poll() as
> a top half to wake up the thread that polls the sensor for
> new data, have the thread call iio_trigger_poll_chained()
> after determining that is is the proper source of the
> interrupt. This is modelled on drivers/iio/accel/mma8452.c
> which is already using a properly threaded interrupt handler.
> 
> In order to get the same precision in timestamps as
> previously, where samples would be timestamped in the
> poll function pf->timestamp when calling
> iio_trigger_generic_data_rdy_poll() we introduce a
> local timestamp in the sensor data, set it in the top half
> (fastpath) of the interrupt handler and provide that to the
> core when calling iio_push_to_buffers_with_timestamp().
An elegant solution - we'll want something along these lines
in the core when we unwind some of the mess you are working around
here - but that can happen in good time...
> 
> Additionally: if the active scanmask is not set for the
> sensor no IRQs should be enabled and we need to bail out
> with IRQ_NONE. This can happen if spurious IRQs fire when
> installing the threaded interrupt handler.
When you say spurious, you mean from another device?
> 
> Tested with hard interrupt triggers on LIS331DL, then also
> tested with hrtimers on the same sensor by creating a 75Hz
> HRTimer and using it to poll the sensor.
> 
> Cc: Giuseppe Barba <giuseppe.barba@st.com>
> Cc: Denis Ciocca <denis.ciocca@st.com>
> Reported-by: Crestez Dan Leonard <cdleonard@gmail.com>
> Tested-by: Crestez Dan Leonard <cdleonard@gmail.com>
> Fixes: 97865fe41322 ("iio: st_sensors: verify interrupt event to status")
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

I think we have a potential race (be it an unlikely one) against
the disabling of a buffer...  I 'think' taking mlock would prevent
the race, but please check I'm not going crazy!

Otherwise this looks about as good as it can be I think.

Ideally I'd like Denis to take a look at this as well.

Jonathan
> ---
> ChangeLog v5->v6:
> - Set the triggered buffer top half IRQ handler to NULL in all
>   subdrivers (accelerometer, gyro, magnetometer, pressure) as
>   we now use the iio_trigger_poll_chained() call.
> - Add st_sensors_validate_device() to the intrinsic triggers
>   and set as .validate_deice() for all subdrivers. Its purpose
>   is to check that the trigger is indeed provided by this
>   device before we use it.
> - NOTE: this patch is a regression fix and can be applied
>   without 2/2.
> ChangeLog v4->v5:
> - Move the setting of hw_irq_enabled to before the register
>   write to enable interrupts so we avoid a race where this
>   variable could be read in its previous state.
> ChangeLog v3->v4:
> - v3 would not timestamp properly when using a HRTimer to read
>   values from the sensors. This is now fixed.
> - Add a flag to the sensor data indicating whether the hardware
>   interrupt trigger is in use. If this is the case, we use that
>   timestamp. If the hardware trigger is not in use, we just let
>   the poll function read the current time before proceeding to
>   grab the values from the sensor.
> - Move interrupt top/bottom halves to st_sensors_trigger.c so the
>   interrupt code is kept together and easier to understand in
>   context.
> ChangeLog v2->v3:
> - v2 was a total disaster, as iio_trigger_generic_data_rdy_poll()
>   would just call the old bottom half and return IRQ_HANDLED.
>   handle the timestamp locally in the sensor data and restore
>   the usage of the local interrupt thread.
> - I think it works now.
> ChangeLog v1->v2:
> - v1 was missing timestamps since nothing ever stamped them.
>   Restore the timestamps by simply using
>   iio_trigger_generic_data_rdy_poll()
>   as the top half of the threaded interrupt handler.
> ---
>  drivers/iio/accel/st_accel_buffer.c                |  2 +-
>  drivers/iio/accel/st_accel_core.c                  |  1 +
>  drivers/iio/common/st_sensors/st_sensors_buffer.c  | 25 ++-----
>  drivers/iio/common/st_sensors/st_sensors_core.c    |  3 +
>  drivers/iio/common/st_sensors/st_sensors_trigger.c | 80 +++++++++++++++++++++-
>  drivers/iio/gyro/st_gyro_buffer.c                  |  2 +-
>  drivers/iio/gyro/st_gyro_core.c                    |  1 +
>  drivers/iio/magnetometer/st_magn_buffer.c          |  2 +-
>  drivers/iio/magnetometer/st_magn_core.c            |  1 +
>  drivers/iio/pressure/st_pressure_buffer.c          |  2 +-
>  drivers/iio/pressure/st_pressure_core.c            |  1 +
>  include/linux/iio/common/st_sensors.h              |  9 ++-
>  12 files changed, 103 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/iio/accel/st_accel_buffer.c b/drivers/iio/accel/st_accel_buffer.c
> index a1e642ee13d6..7fddc137e91e 100644
> --- a/drivers/iio/accel/st_accel_buffer.c
> +++ b/drivers/iio/accel/st_accel_buffer.c
> @@ -91,7 +91,7 @@ static const struct iio_buffer_setup_ops st_accel_buffer_setup_ops = {
>  
>  int st_accel_allocate_ring(struct iio_dev *indio_dev)
>  {
> -	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
> +	return iio_triggered_buffer_setup(indio_dev, NULL,
>  		&st_sensors_trigger_handler, &st_accel_buffer_setup_ops);
>  }
>  
> diff --git a/drivers/iio/accel/st_accel_core.c b/drivers/iio/accel/st_accel_core.c
> index f06f4329db5b..1d9291116556 100644
> --- a/drivers/iio/accel/st_accel_core.c
> +++ b/drivers/iio/accel/st_accel_core.c
> @@ -649,6 +649,7 @@ static const struct iio_info accel_info = {
>  static const struct iio_trigger_ops st_accel_trigger_ops = {
>  	.owner = THIS_MODULE,
>  	.set_trigger_state = ST_ACCEL_TRIGGER_SET_STATE,
> +	.validate_device = st_sensors_validate_device,
>  };
>  #define ST_ACCEL_TRIGGER_OPS (&st_accel_trigger_ops)
>  #else
> diff --git a/drivers/iio/common/st_sensors/st_sensors_buffer.c b/drivers/iio/common/st_sensors/st_sensors_buffer.c
> index c55898543a47..f1693dbebb8a 100644
> --- a/drivers/iio/common/st_sensors/st_sensors_buffer.c
> +++ b/drivers/iio/common/st_sensors/st_sensors_buffer.c
> @@ -57,31 +57,20 @@ irqreturn_t st_sensors_trigger_handler(int irq, void *p)
>  	struct iio_poll_func *pf = p;
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct st_sensor_data *sdata = iio_priv(indio_dev);
> +	s64 timestamp;
>  
> -	/* If we have a status register, check if this IRQ came from us */
> -	if (sdata->sensor_settings->drdy_irq.addr_stat_drdy) {
> -		u8 status;
> -
> -		len = sdata->tf->read_byte(&sdata->tb, sdata->dev,
> -			   sdata->sensor_settings->drdy_irq.addr_stat_drdy,
> -			   &status);
> -		if (len < 0)
> -			dev_err(sdata->dev, "could not read channel status\n");
> -
> -		/*
> -		 * If this was not caused by any channels on this sensor,
> -		 * return IRQ_NONE
> -		 */
> -		if (!(status & (u8)indio_dev->active_scan_mask[0]))
> -			return IRQ_NONE;
> -	}
> +	/* If we do timetamping here, do it before reading the values */
> +	if (sdata->hw_irq_trigger)
> +		timestamp = sdata->hw_timestamp;
> +	else
> +		timestamp = iio_get_time_ns();
>  
>  	len = st_sensors_get_buffer_element(indio_dev, sdata->buffer_data);
>  	if (len < 0)
>  		goto st_sensors_get_buffer_element_error;
>  
>  	iio_push_to_buffers_with_timestamp(indio_dev, sdata->buffer_data,
> -		pf->timestamp);
> +					   timestamp);
>  
>  st_sensors_get_buffer_element_error:
>  	iio_trigger_notify_done(indio_dev->trig);
> diff --git a/drivers/iio/common/st_sensors/st_sensors_core.c b/drivers/iio/common/st_sensors/st_sensors_core.c
> index dffe00692169..928ee68fcc5f 100644
> --- a/drivers/iio/common/st_sensors/st_sensors_core.c
> +++ b/drivers/iio/common/st_sensors/st_sensors_core.c
> @@ -424,6 +424,9 @@ int st_sensors_set_dataready_irq(struct iio_dev *indio_dev, bool enable)
>  	else
>  		drdy_mask = sdata->sensor_settings->drdy_irq.mask_int2;
>  
> +	/* Flag to the poll function that the hardware trigger is in use */
> +	sdata->hw_irq_trigger = enable;
> +
>  	/* Enable/Disable the interrupt generator for data ready. */
>  	err = st_sensors_write_data_with_mask(indio_dev,
>  					sdata->sensor_settings->drdy_irq.addr,
> diff --git a/drivers/iio/common/st_sensors/st_sensors_trigger.c b/drivers/iio/common/st_sensors/st_sensors_trigger.c
> index da72279fcf99..98bd5b3b868f 100644
> --- a/drivers/iio/common/st_sensors/st_sensors_trigger.c
> +++ b/drivers/iio/common/st_sensors/st_sensors_trigger.c
> @@ -17,6 +17,65 @@
>  #include <linux/iio/common/st_sensors.h>
>  #include "st_sensors_core.h"
>  
> +/**
> + * st_sensors_irq_handler() - top half of the IRQ-based triggers
> + * @irq: irq number
> + * @p: private handler data
> + */
> +irqreturn_t st_sensors_irq_handler(int irq, void *p)
> +{
> +	struct iio_trigger *trig = p;
> +	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
> +	struct st_sensor_data *sdata = iio_priv(indio_dev);
> +
> +	/* Get the time stamp as close in time as possible */
> +	sdata->hw_timestamp = iio_get_time_ns();
> +	return IRQ_WAKE_THREAD;
> +}
> +
> +/**
> + * st_sensors_irq_thread() - bottom half of the IRQ-based triggers
> + * @irq: irq number
> + * @p: private handler data
> + */
> +irqreturn_t st_sensors_irq_thread(int irq, void *p)
> +{
> +	struct iio_trigger *trig = p;
> +	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
> +	struct st_sensor_data *sdata = iio_priv(indio_dev);
> +	int ret;
> +
> +	/*
> +	 * If this trigger is backed by a hardware interrupt and we have a
> +	 * status register, check if this IRQ came from us
> +	 */
> +	if (sdata->sensor_settings->drdy_irq.addr_stat_drdy) {
> +		u8 status;
> +
> +		ret = sdata->tf->read_byte(&sdata->tb, sdata->dev,
> +			   sdata->sensor_settings->drdy_irq.addr_stat_drdy,
> +			   &status);
> +		if (ret < 0) {
> +			dev_err(sdata->dev, "could not read channel status\n");
> +			goto out_poll;
> +		}
> +
> +		/*
> +		 * If this was not caused by any channels on this sensor,
> +		 * return IRQ_NONE
> +		 */
> +		if (!indio_dev->active_scan_mask)
> +			return IRQ_NONE;
I'm wondering if this is the right check...   It might be racey with a buffer
being disabled.

Take mlock around the check perhaps? + the use of it below.  I haven't
thought this through enough to be sure that's sufficient though...

> +		if (!(status & (u8)indio_dev->active_scan_mask[0]))
> +			return IRQ_NONE;
A bitmap comparison might be more elegant. Also I would suggest it would
be neater to mask status to only have the relevant bits - not technically
necessary as those are the only ones that should overlap with the scan_mask
but neater none the less.

> +	}
> +
> +out_poll:
> +	/* It's our IRQ: proceed to handle the register polling */
> +	iio_trigger_poll_chained(p);
> +	return IRQ_HANDLED;
> +}
> +
>  int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
>  				const struct iio_trigger_ops *trigger_ops)
>  {
> @@ -77,9 +136,12 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
>  	    sdata->sensor_settings->drdy_irq.addr_stat_drdy)
>  		irq_trig |= IRQF_SHARED;
>  
> -	err = request_threaded_irq(irq,
> -			iio_trigger_generic_data_rdy_poll,
> -			NULL,
> +	/* Let's create an interrupt thread masking the hard IRQ here */
> +	irq_trig |= IRQF_ONESHOT;
> +
> +	err = request_threaded_irq(sdata->get_irq_data_ready(indio_dev),
> +			st_sensors_irq_handler,
> +			st_sensors_irq_thread,
>  			irq_trig,
>  			sdata->trig->name,
>  			sdata->trig);
> @@ -119,6 +181,18 @@ void st_sensors_deallocate_trigger(struct iio_dev *indio_dev)
>  }
>  EXPORT_SYMBOL(st_sensors_deallocate_trigger);
>  
> +int st_sensors_validate_device(struct iio_trigger *trig,
> +			       struct iio_dev *indio_dev)
> +{
> +	struct iio_dev *indio = iio_trigger_get_drvdata(trig);
> +
> +	if (indio != indio_dev)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(st_sensors_validate_device);
> +
>  MODULE_AUTHOR("Denis Ciocca <denis.ciocca@st.com>");
>  MODULE_DESCRIPTION("STMicroelectronics ST-sensors trigger");
>  MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/gyro/st_gyro_buffer.c b/drivers/iio/gyro/st_gyro_buffer.c
> index d67b17b6a7aa..a5377044e42f 100644
> --- a/drivers/iio/gyro/st_gyro_buffer.c
> +++ b/drivers/iio/gyro/st_gyro_buffer.c
> @@ -91,7 +91,7 @@ static const struct iio_buffer_setup_ops st_gyro_buffer_setup_ops = {
>  
>  int st_gyro_allocate_ring(struct iio_dev *indio_dev)
>  {
> -	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
> +	return iio_triggered_buffer_setup(indio_dev, NULL,
>  		&st_sensors_trigger_handler, &st_gyro_buffer_setup_ops);
>  }
>  
> diff --git a/drivers/iio/gyro/st_gyro_core.c b/drivers/iio/gyro/st_gyro_core.c
> index be9057e89dc3..242a3e3c88e4 100644
> --- a/drivers/iio/gyro/st_gyro_core.c
> +++ b/drivers/iio/gyro/st_gyro_core.c
> @@ -408,6 +408,7 @@ static const struct iio_info gyro_info = {
>  static const struct iio_trigger_ops st_gyro_trigger_ops = {
>  	.owner = THIS_MODULE,
>  	.set_trigger_state = ST_GYRO_TRIGGER_SET_STATE,
> +	.validate_device = st_sensors_validate_device,
>  };
>  #define ST_GYRO_TRIGGER_OPS (&st_gyro_trigger_ops)
>  #else
> diff --git a/drivers/iio/magnetometer/st_magn_buffer.c b/drivers/iio/magnetometer/st_magn_buffer.c
> index ecd3bd0a9769..0a9e8fadfa9d 100644
> --- a/drivers/iio/magnetometer/st_magn_buffer.c
> +++ b/drivers/iio/magnetometer/st_magn_buffer.c
> @@ -82,7 +82,7 @@ static const struct iio_buffer_setup_ops st_magn_buffer_setup_ops = {
>  
>  int st_magn_allocate_ring(struct iio_dev *indio_dev)
>  {
> -	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
> +	return iio_triggered_buffer_setup(indio_dev, NULL,
>  		&st_sensors_trigger_handler, &st_magn_buffer_setup_ops);
>  }
>  
> diff --git a/drivers/iio/magnetometer/st_magn_core.c b/drivers/iio/magnetometer/st_magn_core.c
> index 62036d2a9956..8250fc322c56 100644
> --- a/drivers/iio/magnetometer/st_magn_core.c
> +++ b/drivers/iio/magnetometer/st_magn_core.c
> @@ -572,6 +572,7 @@ static const struct iio_info magn_info = {
>  static const struct iio_trigger_ops st_magn_trigger_ops = {
>  	.owner = THIS_MODULE,
>  	.set_trigger_state = ST_MAGN_TRIGGER_SET_STATE,
> +	.validate_device = st_sensors_validate_device,
>  };
>  #define ST_MAGN_TRIGGER_OPS (&st_magn_trigger_ops)
>  #else
> diff --git a/drivers/iio/pressure/st_pressure_buffer.c b/drivers/iio/pressure/st_pressure_buffer.c
> index 2ff53f222352..99468d0a64e7 100644
> --- a/drivers/iio/pressure/st_pressure_buffer.c
> +++ b/drivers/iio/pressure/st_pressure_buffer.c
> @@ -82,7 +82,7 @@ static const struct iio_buffer_setup_ops st_press_buffer_setup_ops = {
>  
>  int st_press_allocate_ring(struct iio_dev *indio_dev)
>  {
> -	return iio_triggered_buffer_setup(indio_dev, &iio_pollfunc_store_time,
> +	return iio_triggered_buffer_setup(indio_dev, NULL,
>  		&st_sensors_trigger_handler, &st_press_buffer_setup_ops);
>  }
>  
> diff --git a/drivers/iio/pressure/st_pressure_core.c b/drivers/iio/pressure/st_pressure_core.c
> index 9e9b72a8f18f..b48285739246 100644
> --- a/drivers/iio/pressure/st_pressure_core.c
> +++ b/drivers/iio/pressure/st_pressure_core.c
> @@ -425,6 +425,7 @@ static const struct iio_info press_info = {
>  static const struct iio_trigger_ops st_press_trigger_ops = {
>  	.owner = THIS_MODULE,
>  	.set_trigger_state = ST_PRESS_TRIGGER_SET_STATE,
> +	.validate_device = st_sensors_validate_device,
>  };
>  #define ST_PRESS_TRIGGER_OPS (&st_press_trigger_ops)
>  #else
> diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
> index d029ffac0d69..99403b19092f 100644
> --- a/include/linux/iio/common/st_sensors.h
> +++ b/include/linux/iio/common/st_sensors.h
> @@ -223,6 +223,8 @@ struct st_sensor_settings {
>   * @get_irq_data_ready: Function to get the IRQ used for data ready signal.
>   * @tf: Transfer function structure used by I/O operations.
>   * @tb: Transfer buffers and mutex used by I/O operations.
> + * @hw_irq_trigger: if we're using the hardware interrupt on the sensor.
> + * @hw_timestamp: Latest timestamp from the interrupt handler, when in use.
>   */
>  struct st_sensor_data {
>  	struct device *dev;
> @@ -247,6 +249,9 @@ struct st_sensor_data {
>  
>  	const struct st_sensor_transfer_function *tf;
>  	struct st_sensor_transfer_buffer tb;
> +
> +	bool hw_irq_trigger;
> +	s64 hw_timestamp;
>  };
>  
>  #ifdef CONFIG_IIO_BUFFER
> @@ -260,7 +265,8 @@ int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
>  				const struct iio_trigger_ops *trigger_ops);
>  
>  void st_sensors_deallocate_trigger(struct iio_dev *indio_dev);
> -
> +int st_sensors_validate_device(struct iio_trigger *trig,
> +			       struct iio_dev *indio_dev);
>  #else
>  static inline int st_sensors_allocate_trigger(struct iio_dev *indio_dev,
>  				const struct iio_trigger_ops *trigger_ops)
> @@ -271,6 +277,7 @@ static inline void st_sensors_deallocate_trigger(struct iio_dev *indio_dev)
>  {
>  	return;
>  }
> +#define st_sensors_validate_device NULL
>  #endif
>  
>  int st_sensors_init_sensor(struct iio_dev *indio_dev,
> 

Re: [PATCH 2/2 v6] iio: st_sensors: read surplus samples in trigger

[Jonathan Cameron]

On 11/05/16 07:01, Linus Walleij wrote:
> On Tue, May 10, 2016 at 6:40 PM, Crestez Dan Leonard
> <leonard.crestez@intel.com> wrote:
>> [Me]
>>> ChangeLog v5->v6:
>>> - Add a loop counter to the threaded value poll function: let's
>>>   just loop here for at maximum 10 loops before we exit and
>>>   let the thread re-trigger if more interrupts arrived.
>>
>> This only serves to hide the problem.
> 
> Not really. The system can preempt after exiting the thread but
> before processing the next set of samples.
> 
>> Version 5 seems preferable. Or
>> even just adding msleep(10) in that infinite loop.
> 
> That provides a preemption point I guess but usleep_range()
> is usually preferrable for such cases. 10ms is way to long
> time to wait, because the max sample frequency will be
> 1/10ms = 100Hz and some ST sensors I have support
> 1kHz updates even. The usleep range would need to be
> very short.
These devices are getting slower in their old age - the venerable lis3l02dq
supports 4.48 kHz.

See the thread in response to Leonard's patch.  I 'fear' we may need a combination
of the two approaches.  Perhaps one of the ST guys can confirm these devices
really are doing level interrupts in all cases as it gets even more complex
if only some devices are...

> 
> Yours,
> Linus Walleij
> --
> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [PATCH 1/2 v6] iio: st_sensors: switch to a threaded interrupt

[Linus Walleij]

On Sat, May 14, 2016 at 6:48 PM, Jonathan Cameron <jic23@kernel.org> wrote:
> On 10/05/16 10:00, Linus Walleij wrote:

>> +             /*
>> +              * If this was not caused by any channels on this sensor,
>> +              * return IRQ_NONE
>> +              */
>> +             if (!indio_dev->active_scan_mask)
>> +                     return IRQ_NONE;
>
> I'm wondering if this is the right check...   It might be racey with a buffer
> being disabled.

It needs to be there if we get a spurious interrupt before any channels
are enabled, as at that point ->active_scan_mask is NULL and
will cause a segfault also it bit me for real, so not just a theoretical
point.

> Take mlock around the check perhaps? + the use of it below.  I haven't
> thought this through enough to be sure that's sufficient though...

I don't see how ->mlock would help? The code in e.g.
iio_enable_buffers() is just optimistically setting ->active_scan_mask
with no locks held. This NULL check is *only* for the case where an
IRQ fires after the buffer has been registered but before the buffer is enabled,
(or after the buffer is disabled, but the IRQ still fires for some reason)
it seems safe to me?

>> +             if (!(status & (u8)indio_dev->active_scan_mask[0]))
>> +                     return IRQ_NONE;
>
> A bitmap comparison might be more elegant.

I guess, but the whole logic of these ST sensors drivers are quite brutally
just assuming bits 0,1,2 in the active_scan_mask is equal to
axis x,y,z, c.f.:

st_accel_buffer_postenable():
err = st_sensors_set_axis_enable(indio_dev,
                                        (u8)indio_dev->active_scan_mask[0]);
(...)

Which goes here:

int st_sensors_set_axis_enable(struct iio_dev *indio_dev, u8 axis_enable)
{
        struct st_sensor_data *sdata = iio_priv(indio_dev);

        return st_sensors_write_data_with_mask(indio_dev,
                                sdata->sensor_settings->enable_axis.addr,
                                sdata->sensor_settings->enable_axis.mask,
                                axis_enable);
}

I.e. just writing the value of active_scan_mask into the register as you can
see. (Not elegant, but I did not write this code.)

The status check follows the same 1:1 mapping pattern so as to not
fuzz things up. If we change that we should make a separate patch
fixing this design pattern to do bitmap operations everywhere I think.

> Also I would suggest it would
> be neater to mask status to only have the relevant bits - not technically
> necessary as those are the only ones that should overlap with the scan_mask
> but neater none the less.

It relies on the same pattern and any other bits than 0,1,2 of active_scan_mask
being zero indeed. I can &= 3 the status register first, I'll send a patch with
that change once we agree on the rest.

Yours,
Linus Walleij

Re: [PATCH 1/2 v6] iio: st_sensors: switch to a threaded interrupt

[jic23]

On 15.05.2016 20:10, Linus Walleij wrote:
> On Sat, May 14, 2016 at 6:48 PM, Jonathan Cameron <jic23@kernel.org> 
> wrote:
>> On 10/05/16 10:00, Linus Walleij wrote:
> 
>>> +             /*
>>> +              * If this was not caused by any channels on this 
>>> sensor,
>>> +              * return IRQ_NONE
>>> +              */
>>> +             if (!indio_dev->active_scan_mask)
>>> +                     return IRQ_NONE;
>> 
>> I'm wondering if this is the right check...   It might be racey with a 
>> buffer
>> being disabled.
> 
> It needs to be there if we get a spurious interrupt before any channels
> are enabled, as at that point ->active_scan_mask is NULL and
> will cause a segfault also it bit me for real, so not just a 
> theoretical
> point.
Absolutely need a check - this just feels like a slight abuse of a field
where we've never carefully controlled the timing...  Whilst it's 
clearly
related to whether we are ready for an interrupt it might not be the 
only
related field - i.e. we might break it in the future.

Still I don't have a better idea right now so lets go with this.
> 
>> Take mlock around the check perhaps? + the use of it below.  I haven't
>> thought this through enough to be sure that's sufficient though...
> 
> I don't see how ->mlock would help? The code in e.g.
> iio_enable_buffers() is just optimistically setting ->active_scan_mask
> with no locks held. This NULL check is *only* for the case where an
> IRQ fires after the buffer has been registered but before the buffer is 
> enabled,
> (or after the buffer is disabled, but the IRQ still fires for some 
> reason)
> it seems safe to me?
Sorry, I didn't put that clearly at all.  The mlock isn't a replacement
for the check, it was to avoid a race on removal.
disable_buffers will reset active_scan_mask to NULL.  The issue arises 
if
that happens between your check above and dereferencing active_scan_mask
below.

update_buffers which is responsible for 'most' calls of the relevant 
code
holds mlock so that would prevent this race.  Unfortunately 
disable_all_buffers
doesn't which is nasty and should probably be fixed.
> 
>>> +             if (!(status & (u8)indio_dev->active_scan_mask[0]))
>>> +                     return IRQ_NONE;
>> 
>> A bitmap comparison might be more elegant.
> 
> I guess, but the whole logic of these ST sensors drivers are quite 
> brutally
> just assuming bits 0,1,2 in the active_scan_mask is equal to
> axis x,y,z, c.f.:
> 
> st_accel_buffer_postenable():
> err = st_sensors_set_axis_enable(indio_dev,
>                                         
> (u8)indio_dev->active_scan_mask[0]);
> (...)
> 
> Which goes here:
> 
> int st_sensors_set_axis_enable(struct iio_dev *indio_dev, u8 
> axis_enable)
> {
>         struct st_sensor_data *sdata = iio_priv(indio_dev);
> 
>         return st_sensors_write_data_with_mask(indio_dev,
>                                 
> sdata->sensor_settings->enable_axis.addr,
>                                 
> sdata->sensor_settings->enable_axis.mask,
>                                 axis_enable);
> }
> 
> I.e. just writing the value of active_scan_mask into the register as 
> you can
> see. (Not elegant, but I did not write this code.)
> 
> The status check follows the same 1:1 mapping pattern so as to not
> fuzz things up. If we change that we should make a separate patch
> fixing this design pattern to do bitmap operations everywhere I think.
Fair enough.
> 
>> Also I would suggest it would
>> be neater to mask status to only have the relevant bits - not 
>> technically
>> necessary as those are the only ones that should overlap with the 
>> scan_mask
>> but neater none the less.
> 
> It relies on the same pattern and any other bits than 0,1,2 of 
> active_scan_mask
> being zero indeed. I can &= 3 the status register first, I'll send a 
> patch with
> that change once we agree on the rest.
Sure.
> 
> Yours,
> Linus Walleij
> --
> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html