Reading an I2C device from the Linux MCU used a separate write(2)
to select the target register & read(2) to get the value(s). This
implementation uses ioctl(file, I2C_RDWR, ...) to skip a large bus idle
period and extra process sleep by combining them like the stm32.
I2C_RDRW requires I2C_FUNC_I2C flag in the I2C driver. I2C_FUNC_I2C
is defined in:
BCM2835: Pi 1 Models A, A+, B, B+, the Raspberry Pi Zero, the
Raspberry Pi Zero W, and the Raspberry Pi Compute Module 1
BCM2836: Pi 2 Model B
Identical to BCM2835 except Cortex
BCM2837: Pi 3 Model B, later models of the Raspberry Pi 2 Model B,
and the Raspberry Pi Compute Module 3
BCM2837B0: Pi 3 Models A+, B+, and the Raspberry Pi Compute Module 3+
BCM2711: Pi 4 Model B, the Raspberry Pi 400, and the Raspberry Pi
Compute Module 4
RK3xxx: Rockchips SoCs NanoPi, RockPi, Tinker, etc.
SUNXI: H2, H3, etc. Orange Pi
AMLOGIC: S905x, Banana Pi, Odroid, etc.
TEGRA: NVidia Jetson etc.
MediaTek: Several SBCs in other ranges
Signed-off-by: Matthew Swabey <matthew@swabey.org>
9d77f44995