[PATCH v4 0/3] Support ROHM BD79112 ADC

Matti Vaittinen
2025-09-10T11:23:51Z

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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.

Revision history:
v3 => v4:
- Fix Kconfig dependency (I2C => SPI)
- Styling as suggested by Andy and Jonathan
- Moved I/O documentation comment and read/write functions next to each
other and tried clarifying the comment

v2 => v3:
- Mostly cosmetic changes to the driver
- dt-bindings and MAINTAINERS unchanged

v1 => v2:
- Plenty of fixes to the driver (thanks to reviewers, Andy and David)
- Add gpio-controller information to the device-tree bindings

See individual patches for more accurate changelog

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

.../devicetree/bindings/iio/adc/rohm,bd79112.yaml | 104 ++++
MAINTAINERS | 3 +-
drivers/iio/adc/Kconfig | 10 +
drivers/iio/adc/Makefile | 1 +
drivers/iio/adc/rohm-bd79112.c | 553 +++++++++++++++++++++
5 files changed, 670 insertions(+), 1 deletion(-)
---
base-commit: d1487b0b78720b86ec2a2ac7acc683ec90627e5b
change-id: 20250910-bd79112-436a087a5013

Best regards,
--
Matti Vaittinen <mazziesaccount@gmail.com>

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