iio: st_sensors: switch to a threaded interrupt

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.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
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>
Tested-by: Jonathan Cameron <jic23@kernel.org>
Fixes: 97865fe41322 ("iio: st_sensors: verify interrupt event to status")
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

1 files changed, 8 insertions, 1 deletions

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,