Re: [PATCH v2] hw/net/can: Add mcp25625 model

[Ben Dooks]

On 17/03/2023 14:11, Pavel Pisa wrote:
> Hello Ben,
>
> thanks for update.
>
> On Thursday 16 of March 2023 13:41:13 Ben Dooks wrote:
> > From: Ben Dooks <ben.dooks@sifive.com>
> >
> > Add support for Microchip MCP25625 SPI based CAN controller which is
> > very similar to the MCP2515 (and covered by the same Linux driver).
> >
> > This can be added to any machine with SPI support in the machine
> > model file.
> >
> > Example for using this when configured into a machine:
> >
> >         -object can-bus,id=canbus0 \
> >         -object can-host-socketcan,id=canhost0,if=vcan0,canbus=canbus0 \
> >         -global driver=mcp25625,property=canbus,value=canbus0
> >
> > There is tracing support with --trace "*mcp25*"
>
> Code looks good, I have patched actual QEMU sources and build
> it successfully with your change.
>
> I have not seen any warning.
>
> I would like to test the mcp25625 CAN functionality.
>
> I would prefer against some target which is already available
> in QEMU and Linux kernel mainlines, so if somebody can suggest
> some ARM which can connect SPI/SSI device it would be great.
>
> I have setup /srv/nfs/debian-riscv64 chroot and used
> it to prepare minimal 3 MB ramdisk.cpio with busybox
> and full GLIBC and ip package.
>
> I can run it with Debian provided RISC-V kernel
> under QEMU compiled with your mcp25625 chip emulation
>
> qemu-system-riscv64 -m 1G -M sifive_u -smp 2 \
>        -initrd ramdisk.cpio \
>        -kernel vmlinux-6.1.0-6-riscv64 \
>        -nographic \
>        -object can-bus,id=canbus0 \
>        -object can-host-socketcan,id=canhost0,if=can0,canbus=canbus0 \
>        -global driver=mcp25625,property=canbus,value=canbus0
>
> I can see
>
> /sys/bus/platform/devices/10040000.spi
> /sys/bus/platform/devices/10050000.spi
>
> I can run
>
>    modprobe spi-sifive.ko
>
> [   41.524160] sifive_spi 10040000.spi: mapped; irq=21, cs=1
> [   41.529305] sifive_spi 10050000.spi: mapped; irq=22, cs=1
>
>    modprobe mcp251x.ko
>
> I can imagine to build device tree overlay and setup it from within
> kernel if the device is already mapped
>
>    cd /sys/kernel/config/device-tree/overlays
>    [ -d  sifive_u-mcp25625 ] && rmdir sifive_u-mcp25625
>    mkdir sifive_u-mcp25625
>    cd sifive_u-mcp25625
>    cat sifive_u-mcp25625.dtbo >dtbo
>    echo 1 >status
>
> which is what we do with CTU CAN FD ip on Zynq system
> to run PL/FPGA update.
>
> But from QEMU info qtree, I see that device is not mapped in QEMU...
> Which is logic...
>
> So please, can you send instruction how to proceed forward.
>
> Do you have DTB prepared for testing or something similar?
>
> In a longer term perspective, it would be ideal to provide
> some update for documentation, how to use mcp25625 emulation
>
>    https://www.qemu.org/docs/master/system/devices/can.html
>
> By the way, if the Raspberry Pi emulation does not provide
> right SPI emulation as you have noticed, what about BeagleBoneBlack?

At the moment it seems that the as a whole qemu doesn't have a good
way of adding a generic spi device to a bus.

> Does it support SPI? It could be good target to test that mcp25625
> chip emulation is portable..

I've pushed our test branch out to:
https://gitlab.com/CodethinkLabs/qemu/-/commits/mcp25625_test

That adds an spi channel to the sifive_u machine and puts the
right dtb entry in there.

--
Ben Dooks                               http://www.codethink.co.uk/
Senior Engineer                         Codethink - Providing Genius

https://www.codethink.co.uk/privacy.html