[PATCH RFC 0/9] iio: Introduce new timestamp grabbing APIs

[Gyeyoung Baek <gye976@gmail.com>]

Support automatic timestamp grabbing by passing `true` to the `timestamp_enabled` parameter of `iio_triggered_buffer_setup_new()`.
So consumer drivers don't need to set `iio_pollfunc_store_time()` as either the tophalf or bottomhalf manually.

For this, triggers must indicate whether they will call `poll()`, `poll_nested()`, or both before
calling `iio_trigger_register()`. This is necessary because the consumer's handler does not know
in advance which trigger will be attached.

Once `iio_trigger_attach_poll_func()` is called, a timestamp is grabbed in either the
tophalf or bottomhalf based on the trigger's type (POLL or POLL_NESTED). If the trigger
supports both (e.g., at91-sama5d2-adc.c), it is treated as POLL_NESTED since the consumer's
tophalf is not invoked in poll_nested(), but the bottomhalf always is.

If the attached trigger supports timestamp grabbing itself, the consumer does not need to handle it.
Instead, the consumer's `poll_func` pointer is passed to the trigger, which can then store the
timestamp directly into consumer. Trigger drivers can pass timestamp values to consumers in a consistent
interface using the new API `iio_trigger_store_time()`.

Tested on qemu, with dummy and trig-sysfs drivers tweaked for testing.

Signed-off-by: Gyeyoung Baek <gye976@gmail.com>
---
Gyeyoung Baek (9):
      iio: buffer: Fix checkpatch.pl warning
      iio: consumer: Define timestamp-related structures and constants
      iio: consumer: Add new APIs of triggered_buffer_setup() family
      iio: consumer: Add new API iio_poll_func_register()
      iio: consumer: Add new API iio_pollfunc_get_timestamp()
      iio: trigger: Define timetamp-related structures and constants
      iio: trigger: Add new API iio_trigger_attach_timestamp()
      iio: trigger: Add new API iio_trigger_store_time()
      iio: rpr0521: Use new timestamp-related APIs

 drivers/iio/buffer/industrialio-triggered-buffer.c |  84 ++++++++++++-
 drivers/iio/industrialio-trigger.c                 | 135 ++++++++++++++++++++-
 drivers/iio/light/rpr0521.c                        |  22 +---
 include/linux/iio/trigger.h                        |  16 ++-
 include/linux/iio/trigger_consumer.h               |  23 ++++
 include/linux/iio/triggered_buffer.h               |  25 ++++
 6 files changed, 283 insertions(+), 22 deletions(-)
---
base-commit: 43a9eee06bf8a8535d8709b29379bec8cafcab56
change-id: 20250518-timestamp-a899e78e07e3

Best regards,
-- 
Gyeyoung Baek <gye976@gmail.com>