[RFC,v4,0/3] Virtio SPI Linux driver

Message

Haixu Cui April 1, 2025, 3:36 a.m. UTC

This is the 4th RFC version of a virtio SPI Linux driver which is
intended to be compliant with the upcoming virtio specification
version 1.4. The specification can be found in repository
https://github.com/oasis-tcs/virtio-spec.git branch virtio-1.4.
 
Changes between 3rd and 4th virtio SPI driver RFC:
- Remove the logic code for statically creating SPI devices through
  the spi_new_device function.
- Add ACPI support.
- According to Hillf Danton's comment, use init_completion instead of
reinit_completion in virtio_spi_transfer_one function.
 
Changes between 2nd and 3rd virtio SPI driver RFC:
- Order header inclusion alphabetically.
- Add Viresh Kumar's "signed-off" to the header files.
- Rework virtio_spi_one_transfer
  - Rework the delays according to Haixu Cui's advise. Delays are now
    handled in a new sub-function virtio_spi_set_delays.
  - Minor change: Re-formulate arguments of sg_init_one.
- Rework virtio_spi_probe
  - Replace some goto in error paths by return.
  - Add spi_unregister_controller to an error path. Abstained from
    using devm_spi_register_controller to keep order of
    de-initialization in virtio_spi_remove.
  - Add deletion of vqueue to all error paths taken after the virtqueues
    have been initialized.
 
Changes between 1st and 2nd virtio SPI driver RFC:
- Update from virtio SPI draft specification V4 to V10.
- Incorporate review comments gotten from the community.
- A proposal for a performance enhancement having more than only one SPI
message in flight had to be kept out. The more complicated code would
have caused an unacceptable project risk now.
 
The virtio SPI driver was smoke tested on qemu using Qualcomm's
target hardware providing a physical SPI backend device, based on
vhost-user protocol. Take vhost-device-spi as the vhost-user backend
and qemu integrated with vhost-user-spi implementation as the vhost-user
frontend. The Linux version used for testing is 6.12.