Re: [PATCH v8 3/3] HID: cp2112: Fwnode Support

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On Mon, Mar 6, 2023 at 11:49 AM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
>
> On Thu, Mar 02, 2023 at 06:06:06PM +0100, Benjamin Tissoires wrote:
> > On Mar 01 2023, Andy Shevchenko wrote:
> > > On Tue, Feb 28, 2023 at 01:05:54PM -0600, Daniel Kaehn wrote:
>
> ...
>
> > > [1]: https://stackoverflow.com/a/60855157/2511795
> >
> > Thanks Andy for your help here, and thanks for that link.
> >
> > I am trying to test Danny's patch as I want to use it for my HID CI,
> > being an owner of a CP2112 device myself.
> >
> > The current setup is using out of the tree patches [2] which are
> > implementing a platform i2c-hid support and some manual addition of a
> > I2C-HID device on top of it. This works fine but gets busted every now
> > and then when the tree sees a change that conflicts with these patches.
> >
> > So with Danny's series, I thought I could have an SSDT override to
> > declare that very same device instead of patching my kernel before
> > testing it.
> >
> > Of course, it gets tricky because I need to run that under qemu.
> >
> > I am currently stuck at the "sharing the firmware_node from usb with
> > HID" step and I'd like to know if you could help me.
> >
> > On my laptop, if I plug the CP2112 (without using a USB hub), I can get:
> >
> > $> ls -l /sys/bus/hid/devices/0003:10C4:EA90.*
> >   lrwxrwxrwx. 1 root root 0 Mar  2 17:02 /sys/bus/hid/devices/0003:10C4:EA90.0079 -> ../../../devices/pci0000:00/0000:00:14.0/usb2/2-9/2-9:1.0/0003:10C4:EA90.0079
> > $> ls -l /sys/bus/usb/devices/2-9*/firmware_node
> >   lrwxrwxrwx. 1 root root 0 Mar  2 17:03 /sys/bus/usb/devices/2-9:1.0/firmware_node -> ../../../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:15/device:16/device:25
> >   lrwxrwxrwx. 1 root root 0 Mar  2 17:02 /sys/bus/usb/devices/2-9/firmware_node -> ../../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:15/device:16/device:25
> >
> > So AFAIU the USB device is properly assigned a firmware node. My dsdt
> > also shows the "Device (RHUB)" and I guess everything is fine.
>
> Yes, so far so good.
>
> > However, playing with qemu is not so easy.
> >
> > I am running qemu with the following arguments (well, almost because I
> > have a wrapper script on top of it and I also run the compiled kernel
> > from the current tree):
> >
> > #> qemu-system-x86_64 -bios /usr/share/edk2/ovmf/OVMF_CODE.fd \
> >                       -netdev user,id=hostnet0 \
> >                       -device virtio-net-pci,netdev=hostnet0 \
> >                       -m 4G \
> >                       -enable-kvm \
> >                       -cpu host \
> >                       -device qemu-xhci -usb \
> >                       -device 'usb-host,vendorid=0x10c4,productid=0xea90' \
> >                       -cdrom ~/Downloads/Fedora-Workstation-Live-x86_64-37-1.7.iso
>
> Side question, where can I get those blobs from (EDKII and Fedora Live CD)?
> I'm using Debian unstable.

You can install the ovmf package in debian[3], which should have a
similar file.
For the Fedora livecd -> https://getfedora.org/fr/workstation/download/
but any other distribution with a recent enough kernel should show the
same.
  >
>
> > And this is what I get:
> >
> > #> ls -l /sys/bus/hid/devices/0003:10C4:EA90.*
> >   lrwxrwxrwx 1 root root 0 Mar  2 16:10 /sys/bus/hid/devices/0003:10C4:EA90.0001 -> ../../../devices/pci0000:00/0000:00:06.0/usb2/2-1/2-1:1.0/0003:10C4:EA90.0001
> >
> > #> ls -l /sys/bus/usb/devices/2-1*/firmware_node
> >   ls: cannot access '/sys/bus/usb/devices/2-1*/firmware_node': No such file or directory
> >
> > Looking at the DSDT, I do not see any reference to the USB hub, so I
> > wonder if the firmware_node needs to be populated first in the DSDT.
>
> So, where QEMU takes DSDT (ACPI tables in general) from? Can you patch that?
> I believe that's the problem in qemu.

That's a good question and it's one I am not sure I have the answer to.
I would have assumed that the DSDT was in the OVMF firmware, but given
that we can arbitrarily add command line arguments, I believe it
probably just provides a baseline and then we are screwed. The OVMF bios
is compiled only once, so I doubt there is any mechanism to
enable/disable a component in the DSDT, or make it dynamically
generated.

>
> > Also note that if I plug the CP2112 over a docking station, I lose the
> > firmware_node sysfs entries on the host too.
>
> This seems like a lack of firmware node propagating in the USB hub code in
> the Linux kernel.

That would make a lot of sense.

FWIW, in the VM I see a firmware node on the pci controller itself:
#> ls -l /sys/devices/pci0000\:00/0000\:00\:06.0/firmware_node
   lrwxrwxrwx 1 root root 0 Mar  6 12:24 /sys/devices/pci0000:00/0000:00:06.0/firmware_node -> ../../LNXSYSTM:00/LNXSYBUS:00/PNP0A03:00/device:07

And one the host, through a USB hub:

#> ls -l /sys/bus/hid/devices/0003:10C4:EA90.*
   lrwxrwxrwx. 1 root root 0 Mar  6 13:26 /sys/bus/hid/devices/0003:10C4:EA90.007C -> ../../../devices/pci0000:00/0000:00:14.0/usb2/2-8/2-8.2/2-8.2.4/2-8.2.4:1.0/0003:10C4:EA90.007C
#> ls -l /sys/bus/usb/devices/2-8*/firmware_node
   lrwxrwxrwx. 1 root root 0 Mar  2 16:53 /sys/bus/usb/devices/2-8:1.0/firmware_node -> ../../../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:15/device:16/device:1e
   lrwxrwxrwx. 1 root root 0 Mar  2 16:53 /sys/bus/usb/devices/2-8/firmware_node -> ../../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:15/device:16/device:1e

Note that the firmware node propagation stopped at 2-8, and 2.8.2 is not
having a firmware node.


>
> > Do you think it would be achievable to emulate that over qemu and use a
> > mainline kernel without patches?
>
> As long as qemu provides correct DSDT it should work I assume.

Just to be sure I understand, for this to work, we need the DSDT to
export a "Device(RHUB)"?
Or if we fix the USB fw_node propagation, could we just overwrite
"\_SB_.PCI0.S30_"?  "\_SB_.PCI0.S30_" is the name the ACPI is giving to
the USB port in my VM case AFAIU.

Cheers,
Benjamin

>
> > [2] https://gitlab.freedesktop.org/bentiss/gitlab-kernel-ci/-/tree/master/VM

[3] https://packages.debian.org/buster/all/ovmf/filelist