Add support for AD4052 ADC Family

[gastmaier]

PR Description

Add:

• driver support for D4052/AD4058/AD4050/AD4056 (16-bit/12-bit SAR ADC SPI)
• devicetree binding

Optional:

• sample devicetree for coraz7s
• kconfig imply driver

Features:

• Single shot using gpio as ADC CNV
• Buffer readings using AXI PWM ADC CNV and ADC GP1 Data Ready as AXI SPI Engine Offload Trigger
• Monitor mode with ADC GP0 as interrupt trigger (either IIO threshold direction event)
  • User should do register access to get event details.
• Functional modes via oversampling config: Sample Mode (0/1) or Burst Averaging Mode (>1)
  • Burst Avg enables configuring averaging filter length value (AVG_CONFIG.AVG_WIN_LEN)
• DEVICE_CONFIG.POWER_MODE : put device on sleep at pm_runtime ops.
• TIMER_CONFIG.FS_BURST_AUTO : configure burst avg enable and trigger mode sample rates via channel sampling frequency config.

Overall, the highlight of this device is the monitor capability, leveraged by the autonomous trigger mode and exposed as IIO Event.

Linux driver doc:

• live: https://gastmaier.github.io/documentation/linux/drivers/iio-adc/ad4052/index.html
• source: https://github.com/gastmaier/documentation/blob/main/docs/linux/drivers/iio-adc/ad4052/index.rst

HDL: analogdevicesinc/hdl#1504
Datasheet: www.analog.com/ad4052
Tested on Coraz7s

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

[gastmaier]

Change log v2 -> v3

• Add "0" (disabled) to oversampling avail list
• Update iic controller dts address