SPI support for the virt platform

[Marcelo Schmitt]

Hi,

I'd like to know the opinion of the QEMU community on some topics.

In 2021, a pair of patch sets for drivers of the Linux IIO subsystem was
proposed based on some QEMU hacks that added virtual devices with which
it was possible to test the proposed modifications to the Linux kernel
[1, 2, 3].

Most Linux IIO drivers connect to the system through either SPI or I2C.
So, it ends up that these buses are needed to do some tests on IIO
drivers. Because of that, those QEMU changes included hacks to the virt
platform to add SPI or I2C buses.

The documentation says that virt is a generic virtual platform [4]. In
this regard, adding more buses to virt could turn the platform into
something less generic. However, if support for SPI/I2C were added, then
it would reduce the effort needed to develop virtual devices to aid
driver testing. Before putting effort to develop something concrete, I'd
like to ask just to make sure:
Would SPI/I2C support be a good addition to QEMU virt?

Another possibility would be to add support for SPI and I2C buses on
Raspberry Pi boards emulation [5]. Would this be a better idea?

Also, the QEMU devices developed could be upstreamed. At first, I
thought that developing virtual devices would be a win-win situation in
which we could extend Linux's test coverage and add support for new QEMU
devices. However, as these would be dummy devices, I'm not sure how QEMU
would benefit from them. Anyhow, I'd appreciate it if anyone could give
a word about that.


Thanks,
Marcelo

[1] https://lore.kernel.org/linux-iio/20210314181511.531414-1-jic23@kernel.org/
[2] https://lore.kernel.org/linux-iio/20210614113507.897732-1-jic23@kernel.org/
[3] https://github.com/jic23/qemu
[4] https://qemu-project.gitlab.io/qemu/system/arm/virt.html
[5] https://qemu-project.gitlab.io/qemu/system/arm/raspi.html