iio: adc: Add support for AD7091R-8

Add support for Analog Devices AD7091R-2, AD7091R-4, and AD7091R-8
low power 12-Bit SAR ADCs with SPI interface.
Extend ad7091r-base driver so it can be used by the AD7091R-8 driver.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/09d1d1c4b39cecc528488efac6094233715f5659.1703013352.git.marcelo.schmitt1@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Add chip_info callback to get conversion result channel

AD7091R-5 and AD7091R-2/-4/-8 have slightly different register field
layout and due to that require different masks for getting the index of
the channel associated with each read.
Add a callback function so the base driver can get correct channel ID
for each chip variant.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/1f7a40b4839b3a1c3f1a0654a1b329bea870feb6.1703013352.git.marcelo.schmitt1@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Set device mode through chip_info callback

AD7091R-5 devices have a few modes of operation (sample, command,
autocycle) which are set by writing to configuration register fields.
Follow up patches will add support for AD7091R-2/-4/-8 which don't have
those operation modes nor the register fields for setting them.
Make ad7091r_set_mode() a callback function of AD7091R chip_info struct
so the base driver can appropriately handle each design without having
to check which actual chip is connected.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/5140336980f66c2c45f05895c3b68e2f65fba1c2.1703013352.git.marcelo.schmitt1@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Remove unneeded probe parameters

With the grouping of ad7091r initialization data and callbacks into the
init_info struct, there is no more need to pass the device name and
register map through probe function parameters as those will be available
in the init_info object.
Remove probe parameters that are not needed anymore.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/090a6b461410a374511a8c73659de28b2665f96b.1703013352.git.marcelo.schmitt1@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Move chip init data to container struct

AD7091R designs may differ on their communication protocol and resources
required for proper setup. Extract what is design specific into a
init_info struct so the base driver can use data and callback functions
from that struct rather than checking which specific chip is connected
during device initialization.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/1aca2261e227474dc58ce26442845947bcde9b14.1703013352.git.marcelo.schmitt1@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Move generic AD7091R code to base driver and header file

Some code generic to AD7091R devices such as channel definitions were in
the AD7091R-5 driver. There was also some generic register definitions
declared in the base driver which would make more sense to be in the
header file.
The device state struct will be needed for the ad7091r8 driver in a
follow up patch so that ought to be moved to the header file as well.
Lastly, a couple of regmap callback functions are also capable of
abstracting characteristics of different AD7091R devices and those are
now being exported to IIO_AD7091R name space.

Move AD7091R generic code either to the base driver or to the header
file so both the ad7091r5 and the ad7091r8 driver can use those
declaration in follow up patches.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/6376fc523ee503d47ec499e2cd2ef13bfb5fd8ba.1703013352.git.marcelo.schmitt1@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Enable internal vref if external vref is not supplied

The ADC needs a voltage reference to work correctly.
Users can provide an external voltage reference or use the chip internal
reference to operate the ADC.
The availability of an in chip reference for the ADC saves the user from
having to supply an external voltage reference, which makes the external
reference an optional property as described in the device tree
documentation.
Though, to use the internal reference, it must be enabled by writing to
the configuration register.
Enable AD7091R internal voltage reference if no external vref is supplied.

Fixes: 260442cc5be4 ("iio: adc: ad7091r5: Add scale and external VREF support")
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/b865033fa6a4fc4bf2b4a98ec51a6144e0f64f77.1703013352.git.marcelo.schmitt1@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r: Allow users to configure device events

AD7091R-5 devices are supported by the ad7091r-5 driver together with
the ad7091r-base driver. Those drivers declared iio events for notifying
user space when ADC readings fall bellow the thresholds of low limit
registers or above the values set in high limit registers.
However, to configure iio events and their thresholds, a set of callback
functions must be implemented and those were not present until now.
The consequence of trying to configure ad7091r-5 events without the
proper callback functions was a null pointer dereference in the kernel
because the pointers to the callback functions were not set.

Implement event configuration callbacks allowing users to read/write
event thresholds and enable/disable event generation.

Since the event spec structs are generic to AD7091R devices, also move
those from the ad7091r-5 driver the base driver so they can be reused
when support for ad7091r-2/-4/-8 be added.

Fixes: ca69300173b6 ("iio: adc: Add support for AD7091R5 ADC")
Suggested-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://lore.kernel.org/r/59552d3548dabd56adc3107b7b4869afee2b0c3c.1703013352.git.marcelo.schmitt1@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7091r5: Add scale and external VREF support

The scale can now be obtained with the "in_voltage_scale" file.
By default, the scale returned corresponds to the internal VREF of 2.5V.

It is possible to use an external VREF (through the REFIN/REFOUT pin of
the chip), by passing a regulator to the driver. The scale will then be
calculated according to the voltage reported by the regulator.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Co-developed-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: Add support for AD7091R5 ADC

AD7091R5 is 4-Channel, I2C, Ultra Low Power,12-Bit ADC.

This driver will also support AD7091R2/4/8 in the future.

Datasheet:
Link: https://www.analog.com/media/en/technical-documentation/data-sheets/ad7091r-5.pdf

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Co-developed-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>