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

Haixu Cui
2024-03-06T07:48:25Z

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
>>
>>