iio:adc:ad76060: Move exports into IIO_AD7606 namespace.

In order to avoid unnecessary pollution of the global symbol namespace
move the core/library functions into a specific namespace and import
that into the various bus specific device drivers that use them.

For more information see https://lwn.net/Articles/760045/

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220130205701.334592-4-jic23@kernel.org

iio: adc: ad7606: Add support for AD7606B ADC

The AD7606B is a 16-bit ADC that supports simultaneous sampling of 8
channels. It is pin compatible to AD7606, but adds extra modes by
writing to the register map.

The AD7606B can be configured to work in software mode by setting all
oversampling pins to high. This mode is selected by default.
The oversampling ratio is configured from the OS_MODE register (address
0x08) with the addition of OS=128 and OS=256 that were not available in
hardware mode.

The device is configured to output data on a single spi channel, but this
configuration must be done right after restart. That is why the delay was
removed for devices which doesn't require it.

Moreover, in software mode, the range gpio has no longer its function.
Instead, the scale can be configured individually for each channel from
the RANGE_CH registers (address 0x03 to 0x06). Besides the already
supported ±10 V and ±5 V ranges, software mode can also accommodate the
±2.5 V range.

Signed-off-by: Stefan Popa <stefan.popa@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: ad7606: Add support for software mode for ad7616

Support for ad7616 running in software was added. In order
to activate the software mode, HW_RNGSEL pins must be pulled low.
Oversampling and input ranges are now configured in corresponding
registers. Ad7616 has multiple scale options when it is configured
in software mode.
Also, in order to support multiple devices in software mode, the spi
calculation of registers address must be generic. Because
the length of address and bit which specifies the read/write operation is
different for every device, calculation of address was made generic.

Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: adc: ad7616: Add support for AD7616 ADC

The AD7616 is a 12-bit ADC with 16 channels.

The AD7616 can be configured to work in hardware mode by controlling it via
gpio pins and read data via spi. No support for software mode yet, but it
is a work in progress.

This device requires a reset in order to update oversampling, so chip info
has got a new attribute to mark this.

The current assumption that this driver makes for AD7616, is that it's
working in Hardware Mode with Serial, Burst and Sequencer modes activated.
To activate them, following pins must be pulled high:
-SER/PAR
-SEQEN
And following must be pulled low:
-WR/BURST
-DB4/SEQEN

Datasheets:
Link: https://www.analog.com/media/en/technical-documentation/data-sheets/ad7616.pdf

Signed-off-by: Beniamin Bia <beniamin.bia@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

staging: iio: adc: ad7606: Move out of staging

Move ad7606 ADC driver out of staging and into the mainline.

Signed-off-by: Stefan Popa <stefan.popa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>