[PATCH 0/3] Support ROHM BD79112 ADC

[Matti Vaittinen <mazziesaccount@gmail.com>]

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Support ROHM BD79112 ADC/GPIO

The ROHM BD79112 is a 12-bit, 32 channel SAR ADC / GPIO IC. Or, a "Signal
Monitor Hub IC" as data-sheet describes it.

Data sheet states the maximum sampling rate to be 1 MSPS, but achieving
this would probably require the SPI and samples to be processed by
something else but the CPU running Linux. This could work with the "SPI
offloading" which has recently landed upstream - but I have no HW to test
this so nothing fancy is implemented here. It's still worth mentioning
if someone needs the speed and wants to try implementing it :)

The SPI protocol is slightly peculiar. Accesses are done in 16-bit
sequences, separated by releasing and re-aquiring the chip-select.

Register write takes 1 such sequence. The 8-bit register data to write,
is stored in the last 8 bits. The high 8 bits contain register address
and an I/O-bit which needs to be set for register accesses.

Register read consists of two 16-bit sequences (separated by
chip-select). First sequence has again the register address and an IO
bit in the high byte. Additionally, reads must have a 'read bit' set.
The last 8 bits must be zero. The register data will be carried in the
last 8 bits of the next 16-bit sequence while high bits in reply are zero.

ADC data reading is similar to register reading except:
 - No R/W bit or I/O bit should be set.
 - Register address is replaced by channel number (0 - 31).
 - Reply data is carried in the 12 low bits (instead of 8 bits) of the
   reply sequence.

The protocol is implemented using custom regmap read() and write()
operations.

Other than that, pretty standard device and driver.

Matti Vaittinen (3):
  dt-bindings: iio: adc: ROHM BD79112 ADC/GPIO
  iio: adc: Support ROHM BD79112 ADC/GPIO
  MAINTAINERS: Support ROHM BD79112 ADC

 .../bindings/iio/adc/rohm,bd79112.yaml        | 118 ++++
 MAINTAINERS                                   |   3 +-
 drivers/iio/adc/Kconfig                       |  10 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/rohm-bd79112.c                | 542 ++++++++++++++++++
 5 files changed, 673 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/rohm,bd79112.yaml
 create mode 100644 drivers/iio/adc/rohm-bd79112.c


base-commit: d1487b0b78720b86ec2a2ac7acc683ec90627e5b
-- 
2.51.0


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