[PATCH 0/4][V3] iio: imu: Add support for the ADIS16460 IMU

[Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>]

This changeset adds support for the ADIS16460.

Support for this chip, requires changes in both IIO & SPI, in order to
support configurable/longer CS change delays.

The default CS change delay is 10 uS, while the ADIS16460 requires a
minimum of 16 uS. In order to accomodate this, the SPI transfer struct
requires a `cs_change_delay_usecs` parameter that is used when `cs_change`
is set.

The ADIS library also requires a small update to support the new SPI
`cs_change_delay_usecs`, and after that, support for ADIS16460 is added,
since all the required parts for operating the chip are in the kernel.

Continuing discussion from:
  https://lore.kernel.org/lkml/20190717115109.15168-5-alexandru.ardelean@xxxxxxxxxx/T/

Changelog v2 -> v3:
* for SPI:
  * used `cs_change_delay` instead of `cs_change_delay_usecs` (i.e. removed
    `_usecs` suffix
  * used SPI specific subject line for SPI patch
* for ADIS lib:
  * updated to use the `cs_change_delay`
* for DT:
  * added Rob's `Reviewed-by` tag

Changelog v1 -> v2:
* for SPI:
  * renamed `cs_change_stall_delay_us` -> `cs_change_delay_usecs`
    initial recommendation was `cs_change_delay`, but decided to name this
    `cs_change_delay_usecs`, since the convention for these delays seems
    to add the `_usecs` suffix
* for ADIS lib:
  * renamed `stall_delay` -> `cs_change_delay`
  * removed some assignments of `cs_change_delay`
    where `cs_change` is not set
* for ADIS16460 driver:
  * fixed license
  * adjusted to new `cs_change_delay[_usecs]`

Alexandru Ardelean (4):
  spi: Add optional stall delay between cs_change transfers
  iio: imu: adis: Add support for SPI transfer cs_change_delay
  iio: imu: Add support for the ADIS16460 IMU
  dt-bindings: iio: imu: add bindings for ADIS16460

 .../bindings/iio/imu/adi,adis16460.yaml       |  53 ++
 MAINTAINERS                                   |   8 +
 drivers/iio/imu/Kconfig                       |  12 +
 drivers/iio/imu/Makefile                      |   1 +
 drivers/iio/imu/adis.c                        |   6 +
 drivers/iio/imu/adis16460.c                   | 489 ++++++++++++++++++
 drivers/spi/spi.c                             |   3 +-
 include/linux/iio/imu/adis.h                  |   2 +
 include/linux/spi/spi.h                       |   2 +
 9 files changed, 575 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/devicetree/bindings/iio/imu/adi,adis16460.yaml
 create mode 100644 drivers/iio/imu/adis16460.c

-- 
2.20.1