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

[Haixu Cui]

Hello Harald,

    In current driver, spi_new_device is used to instantiate the virtio 
SPI device, spidevX.Y is created manually, this way seems not flexible 
enough. Besides it's not easy to set the spi_board_info properly.

    Viresh Kumar has standardized the device tree node format for 
virtio-i2c and virtio-gpio:


https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/i2c/i2c-virtio.yaml

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/gpio/gpio-virtio.yaml

    In this way, the driver is unified, board customization only 
depends on the device-tree node. It's easy to bring up spidev automatically.

    Look forward to your opinions. Thanks a lot.

Haixu Cui


On 3/6/2024 1:54 AM, Harald Mommer wrote:
> Hello,
>
> looked again at my tinny setup and I've to add a small correction.
>
> It's not the way that I've no udev at all there. What is in place there 
> is busybox mdev.
>
> Relevant part of /etc/init.d/rcS:
>
> #!/bin/sh
> mount -t proc none /proc
> mount -t sysfs none /sys
> depmod
> modprobe spi-virtio
> mdev -s
> mdev -d
>
> If I kill the "mdev -d" process my small script below does not make the 
> /dev/spidev0.0 device node appear any more. Of course not, there must be 
> some user mode process which does the job in the device directory.
>
> Regards
> Harald Mommer
>
> On 05.03.24 11:57, Harald Mommer wrote:
> > 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