Re: [virtio-dev] Re: [RFC PATCH v3 3/3] SPI: Add virtio SPI driver.

Harald Mommer
2024-03-05T10:58:03Z

Hello,

I took next/stable as base giving the exact tag/sha of the current
next/stable so that it's known what was used as base version even when
next/stable moves. The ordinary next tags are currently not of best
quality, gets better, therefore next/stable now. We were on v6.8-rc7
yesterday with next/stable.

VMM is qemu for the driver you have. But it's a specially modified qemu
which allows that we use our proprietary virtio SPI device as backend.

Proprietary virtio SPI device is started first, this is an own user
process in our architecture. Subsequently the special internal qemu
version is started. The virtio SPI driver is compiled as a module and
inserted manually by a startup script by "modprobe spi-virtio". The
driver goes live immediately.

In this simple setup I do not have udev rules (no service supporting
udev => no rules) so no /dev/spidevX.Y automatically after the driver
went live. What I'm using to test the latest driver before sending it to
the mailing lists is really a naked kernel + a busybox running in a
ramdisk. The udev rule I've sent are used on some more complete setup on
real hardware.

So without udev I have to bring this device up manually:

In /etc/spidev-up.sh there is a script tp bring up /dev/spidev0.0 manually:

#!/bin/sh
SPIDEV=spi0.0
echo spidev > /sys/bus/spi/devices/$SPIDEV/driver_override
echo $SPIDEV > /sys/bus/spi/drivers/spidev/bind

Afterwards there is /dev/spidev0.0.

In linux/tools/spi there are spidev_test.c and spidev_fdx.c. Those
(somewhat hacked locally, and I mean "hacked" to be able to test
somewhat more) are used to play around with /dev/spidev0.0.

I can do this on my Laptop which has no underlying SPI hardware which
could be used as a backend for the virtio SPI device. The proprietary
virtio SPI device has a test mode to support this. Using this test mode
the driver does not communicate with a real backend SPI device but does
an internal simulation. For example, if I do a half duplex read it
always gives back the sequence 01 02 03 ...

For full duplex it gives back what has been read but with letter case
changed, in loopback mode it gives back exactly what was sent. With this
test mode I could develop a driver and parts of the device (device -
real backend communication to an actual SPI device) on a board which had
no user space /dev/spiX.Y available which could have served as backend
for the virtio SPI device on the host.

Slightly different module version is tested on real hardware with the
virtio SPI device not in test mode. "Tested on hardware" means that
device + module work for our special use case (some hardware device
using 8 bit word size) and the project team for which device and driver
have been made did until now not complain.

Regards
Harald Mommer

On 05.03.24 08:46, Haixu Cui wrote:
> Hello Harald,
>
> Thank you for your detailed expatiation. To my knowledge, you took
> Vanilla as the front-end, and VMM is QEMU. Can you please explain
> further how do you test the SPI transfer without the Vanilla userspace
> interface? Thanks again.
>
> Haixu Cui