Re: [PATCH v3 00/14] iio: adc: Add AD7768/AD7768-4 ADC driver support

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Thu, Aug 13, 2026 at 03:56:53PM +0200, Janani Sunil wrote:
> Add support for Analog Devices AD7768 and AD7768-4, 24-bit simultaneous
> sampling Sigma-Delta ADCs with automatic power mode selection.
> 
> Datasheet:
> https://www.analog.com/media/en/technical-documentation/data-sheets/ad7768.pdf
> 
> **Device Overview:**
> The AD7768 is an 8-channel, 24-bit simultaneous sampling ADC. The
> AD7768-4 is a 4-channel variant. Both support configurable power modes,
> programmable decimation filters, and a high-speed serial interface with
> 1, 2, 4, or 8 data output lines. Per-channel offset, gain, and phase
> calibration registers are available.
> 
> **Features Implemented:**
> - Support for AD7768 (8-channel) and AD7768-4 (4-channel) via device
>   match data.
> - Automatic low-noise power mode selection (fast, median, low power)
>   with associated decimation rate and output data rate tables.
> - Per-channel offset, gain, and conversion delay via IIO attributes.
> - SPI communication with custom regmap bus for the device's protocol.
> - IIO backend integration with adi-axi-adc for high-speed data capture.
> - CRC data integrity verification over the serial interface.
> - GPIO auxiliary driver to expose the 5 on-chip GPIO pins.
> - VCM common-mode output exposed through the regulator framework, with
>   runtime PM management while the output is enabled.
> 
> **Patch Summary:**
> 1. Add the AD7768 and AD7768-4 devicetree binding.
> 2. Add the IIO backend CRC operation.
> 3. Initialize the AXI ADC state mutex.
> 4. Implement CRC control in the AXI ADC backend.
> 5. Add core AD7768 and AD7768-4 capture support.
> 6. Add configurable sampling rates, power modes, and filters.
> 7. Add per-channel offset and gain calibration controls.
> 8. Add per-channel conversion delay.
> 9. Expose the VCM output through the regulator framework.
> 10. Register the GPIO auxiliary device from the parent driver.
> 11. Use regmap_test_bits() for single-bit gpio-regmap reads.
> 12. Add optional runtime PM support to gpio-regmap.
> 13. Add the AD7768 GPIO auxiliary driver.
> 14. Add driver documentation.
> 
> **Testing:**
> The driver was compiled and tested on the EVAL-AD7768FMCZ using a
> Zedboard with a mainline kernel.
> 
> **Driver Rationale:**
> The AD7768/AD7768-4 warrants its own driver due to several
> device-specific characteristics:
> 
> 1. A custom SPI framing protocol: register reads and writes use 16-bit
>    frames with embedded read/write bits and register address fields,
>    requiring a custom regmap bus implementation rather than the standard
>    SPI regmap backend.
> 
> 2. A coupled power mode / sample rate model: available output data rates
>    are not a flat list but depend on the active power mode (fast, median,
>    low power), each with its own set of valid decimation rates. This
>    relationship must be managed in the driver.
> 
> 3. Simultaneous sampling across all channels with per-channel calibration
>    registers (24-bit offset, gain, and phase) that are laid out
>    differently between the 8-channel AD7768 and the 4-channel AD7768-4,
>    requiring device-specific register mapping.
> 
> 4. IIO backend integration for high-speed data capture via adi-axi-adc,
>    including CRC data integrity verification over the serial interface.
> 
> 5. On-chip GPIO: 5 general-purpose I/O pins exposed via an auxiliary bus
>    driver, sharing the parent's regmap and runtime PM.

The GPIO driver looks nice, but regmap API should use cleanup.h instead of
custom (legacy) approach.

-- 
With Best Regards,
Andy Shevchenko