Re: [PATCH v1 2/2] iio: adc: Add TI ADS131M0x ADC driver

[Oleksij Rempel <o.rempel@pengutronix.de>]

Hi David,

On Thu, Nov 06, 2025 at 10:57:26AM -0600, David Lechner wrote:
> ...
> 
> > +/**
> > + * ads131m_rmw_reg - Reads, modifies, and writes a single register.
> 
> Any reason we couldn't turn the read/write into a regmap and avoid
> implementing extras like this?

I thought about regmap, but it is a poor fit for this chip.

The problem is the device protocol. It is not a simple register-based device;
it is a frame-based protocol that uses opcodes.

-  Hot Path (Data Read): The main data read (in read_raw) does not access
registers. It sends a NULL opcode frame to read all channel data at once.

-  Cold Path (Setup): Register access (RREG/WREG) is a complex, stateful
3-cycle operation. It is only used in probe for setup.

This leaves two (bad?) options for regmap:

- Mixed Access: Use regmap only for the cold path (probe) and use raw
for the hot path (read_raw). This is messy because we mix two access methods.

- Virtual Registers: Try to model all opcodes (NULL, RREG, WREG) as virtual
registers. This is a very unnatural abstraction for this chip.

Using the regmap dependency just to replace one rmw function that runs only
once at probe seemed like the overkill.

Best Regards,
Oleksij
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