Add support for AD4052 ADC Family

[gastmaier]

Changes to backport to main

driver=drivers/iio/adc/ad4052.c
doc=Documentation/iio/ad4052.rst
bin=Documentation/devicetree/bindings/iio/adc/adi,ad4052.yaml
inc=include/dt-bindings/iio/adc/adi,ad4052.h
abi=Documentation/ABI/testing/sysfs-bus-iio
adi=../linux
up=../../linux-upstream

up2adi () {
        cp $up/$driver $adi/$driver
        cp $up/$doc $adi/$doc
        cp $up/$bin $adi/$bin
        cp $up/$abi $adi/$abi
        cp $up/$inc $adi/$inc
        #sed -i -e 's/iio_device_release_direct(/iio_device_release_direct_mode(/g' \
        #       -e 's/\!iio_device_claim_direct(/iio_device_claim_direct_mode(/g' \
        sed -i -e 's/bool state/int state/' \
               -e 's/linux\/unaligned.h/asm-generic\/unaligned.h/' \
               -e 's/("IIO_DMAENGINE_BUFFER")/(IIO_DMAENGINE_BUFFER)/' $adi/$driver
}

PR Type

• Bug fix (a change that fixes an issue)
• New feature (a change that adds new functionality)
• Breaking change (a change that affects other repos or cause CIs to fail)

PR Checklist

• I have conducted a self-review of my own code changes
• I have tested the changes on the relevant hardware
• I have updated the documentation outside this repo accordingly (if there is the case)

[gastmaier]

Forced pushed to:

• Add support to TIMER_CONFIG.FS_BURST_AUTO
• Only write GP during probe.
• Simplify IRQ Handler, leave to the user to clear the irq, because:
  • Entering config mode causes the irq to unset.
  • Re-entering monitor mode sets the irq back if still outside the threshold range, causing new handler calls.
  • "Ignoring next interrupt" would generate obnoxious logic.

Forced pushed (2) to:

• Invert fs_burst_auto array entries, default all devices to 2MSPS (Yes, this value is -EINVAL for ad4056/ad4058, but is the datasheet reset value)

Forced pushed (3) to:

• Clean-up unused enums.
• Rename ad405x to ad4052 in the dts

[nunojsa]

Here it goes first round of review...

I think this one can be upstreamed without the offload bits

[gastmaier]

Change log v0 -> v1

Review changes:

• Move functional modes from devicetree entry to different OVERSAMPLING_RATIO values, affecting RAW read and buffered.
• Documentation YAML fixes, removal of functional mode.
• Header on alphabetical order.
• Use field_prep
• Remove forward declaration, reorder methods instead.
• Fix cache line aligment.
• Use devm runtime enable, remove manual remove.
• Use dev_err_probe
• General Documentation/.yaml fixes
• Make all regmap_bulk dma safe.
• Remove/simplify switch cases where not needed.
• Instead of using of_node, use spi->irq directly
• Use regmap update bits.
• Use fsleep
• Use oversampling iio property (value 0 is invalid, 1 put on Sample Mode, > 1 Burst Averaging mode)

New:

• Add regmap access tables

Design changes:

• Under IIO Event thrshold enabled (device Monitor Mode), return device access busy for every other access, simplifying logic by not requiring exiting and re-entering mode and having an obscure "monitoring downtime" during access.
• Use oversampling iio prop instead of devicetree entry to switch functional modes.

[nunojsa]

I'm also not sure if gpio is something you should depend on or just select it. I think the single shot reading could be something useful to have even more to make this driver more upstreamable without offload support (we can still some questions about it though).

[nunojsa]

Also one not on the commit message. Style is iio: adc: .... Drop the drivers:

[nunojsa]

I would double check other examples of oversampling. To me this is a 1 or 0 thing. Either it's enabled it not. Your mode variable also just seems to have two states here so the way you're handling val raises some questions.

[gastmaier]

The device supports from 2 to 4096 in powers of 2 samples for avg mode.
Decided to reserve 0 and 1 to disable the feature (return to sample mode)

[gastmaier]

Change log v1 -> v2

Review changes:

• Include all peripheral properties
• Drop cnv-gpio description
• Updated dt-binding commit description
• Replace d32 array by d16/d32 union (requires ignoring misleading checkpatch warning).
• Remove MODULE_IMPORT_NS(IIO_AD4052);
• Add error handling where missing
• remove {} in single statement ifs, coherent style
• Use multiple scan masks for changing precision due to oversampling
• Move all if (st->mode == AD4052_MONITOR_MODE) inside the IIO mutex claim.
• Drop switches where there is only one channel/event type
• Remove unused AD4052_AVERAGING_MODE (would require a timed trigger) and AD4052_CONFIG_MODE (implicit mode outside any reading)
• ad4052_set_avg_filter pass st directly.
• Use different variables instead of the array for the chip_info

Changes:

• Use GPIO interrupt instead of PS IRQ
• All GPIOs are optional, does not require GPIO on KConfig. The user shall bring his own external trigger or short the CS and CNV, for example.
• Move PWM sampling rate to IIO_ATTR
• Move ext fs_burst_auto to channel sampling freq
• Use Data Ready assertions for single shot readings, timeout after 1 second

Extra force push to resolve merge conflict