Merge tag 'iio-for-4.19c' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio into staging-next

Jonathan writes:

Third set of IIO new device support, cleanups and features for the 4.19 cycle

Merge tag 'iio-for-4.19c' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio into staging-next

Jonathan writes:

Third set of IIO new device support, cleanups and features for the 4.19 cycle.

This is a somewhat sneaky late pull request given Linus has announced
a likely 1 week delay. If it is too late I'll resend after the merge
window. I merged in the fixes branch as those are primarily around
things queued for the merge window.

Particulary good to see the output of our Himanshu Jha, a GSOC student
who developed the bme680 driver.

New device support:
* bme680 gas sensor (with temperature, humidity and pressure)
- new driver to support this device
* vcn4000
- support vcnl4200 (lots of rework to allow this)
- ids added for VCNL4010 and VCNL4020 sensors

New features:
* ad9523
- support the various external signal options via gpios.

Cleanups and fixes
* ad_sigma_delta
- unsigned long for a timeout.
* ad9523
- fix a wrong return value that was indicating successful write failed
and might lead to an infinite loop.
* si1133
- fix an impossible test.
- fix an uninitialsed variable by reading from the device in all paths.
* xilinx xadc
- check for return values in clk related functions
- limit the pcap clock frequency to supported ranges.
- stash the irq to avoid calling platform_get_irq from the remove path.
- ensure the irq is actually requested before we enable the hardware to
output it.

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iio: chemical: Add support for Bosch BME680 sensor

Bosch BME680 is a 4-in-1 sensor with temperature, pressure, humidity
and gas sensing capability. It supports both I2C and SPI communication
protoco

iio: chemical: Add support for Bosch BME680 sensor

Bosch BME680 is a 4-in-1 sensor with temperature, pressure, humidity
and gas sensing capability. It supports both I2C and SPI communication
protocol for effective data communication.

The device supports two modes:

1. Sleep mode
2. Forced mode

The measurements only takes place when forced mode is triggered and a
single TPHG cycle is performed by the sensor. The sensor automatically
goes to sleep after afterwards.

The device has various calibration constants/parameters programmed into
devices' non-volatile memory(NVM) during production and can't be altered
by the user. These constants are used in the compensation functions to
get the required compensated readings along with the raw data. The
compensation functions/algorithms are provided by Bosch Sensortec GmbH
via their API[1]. As these don't change during the measurement cycle,
therefore we read and store them at the probe. The default configs
supplied by Bosch are also set at probe.

0-day tested with build success.

GSoC-2018: https://summerofcode.withgoogle.com/projects/#6691473790074880
Mentor: Daniel Baluta
[1] https://github.com/BoschSensortec/BME680_driver
Datasheet:
https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME680-DS001-00.pdf

Note from Jonathan: The compensation functions are 'interesting' and
could do with a tidy up in future. However, they work so we can leave that
for another day.

Cc: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Himanshu Jha <himanshujha199640@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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