Sorry for the late reply, and thank you for the feedback.
The reason I implemented a native PIO_SPI is as follows:

1. Performance and Overhead
   WIZnet chips require very frequent register accesses. In practice, the Python interpreter overhead accumulates and can noticeably reduce throughput and responsiveness. The native implementation removes this overhead and ensures more stable operation.

2. High-Speed Transfer
   Communication with the Ethernet chips often requires SPI clock rates in the several-MHz range. With a Python-only approach it may be difficult to achieve these speeds reliably, whereas a native PIO driver might make it relatively easier to reach them.

3. Precise Frame Control
   WIZnet chips use slightly different SPI framing depending on the model, and they are sensitive to inter-byte gaps and clock timing. A native implementation provides more predictable timing and precise frame handling.

for this use case I found that a native PIO_SPI provides the performance and stability needed.

The W6300 will need library changes for the extra pins to take advantage of the quad SPI?

1. In practice, the Python interpreter overhead accumulates and can noticeably reduce throughput and responsiveness. The native implementation removes this overhead and ensures more stable operation.

Did you try the Python-only version first? I'm worried this is a lot of specific code for us to maintain. Having it in a library of yours using rp2pio directly means you can maintain it easier.

Thanks again for the thoughtful feedback. I wanted to clarify why I proposed a native PIO SPI implementation and ask whether you’d consider accepting it (or advising on the right shape for it).

The design closely follows the Raspberry Pi SDK’s PIO SPI used by the CYW43 Wi-Fi driver, combining PIO state machines with DMA-backed transfers. This architecture is already validated for continuous, high-speed register access on RP2040 and gives deterministic inter-byte timing that WIZnet parts are sensitive to.
Reference: pico-sdk/src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c.
https://github.com/raspberrypi/pico-sdk/blob/a1438dff1d38bd9c65dbd693f0e5db4b9ae91779/src/rp2_common/pico_cyw43_driver/cyw43_bus_pio_spi.c

That reference was key in shaping this design. However, since there was no complete example available for implementing a full PIO SPI interface purely in Python, it was difficult to achieve precise byte-level timing control or continuous DMA-based transfers using Python alone.