Re: ACPI: Can I use I2cSerialBus with a PCI I2C controller?

[Ben Gardner <gardner.ben@gmail.com>]

>> Is there a way to see PCI to ACPI associations?
>
> Yes, the PCI device has a symlink "firmware_node" which points to the
> ACPI device.
>
> Here an example from Skylake system (which uses PCI mode for LPSS
> devices):
>
> # ls -l /sys/bus/pci/devices/0000\:00\:15.1/firmware_node
> lrwxrwxrwx    1 root     root             0 Oct 22 08:00 /sys/bus/pci/devices/0000:00:15.1/firmware_node -> ../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:6f
>
> # cat /sys/bus/pci/devices/0000\:00\:15.1/firmware_node/path
> \_SB_.PCI0.I2C1

I see the problem now.
Your I2C controller is under the PCI0 device on your Skylake system,
mine was not.

So, I moved the definition of all the PCI devices that are on PCI bus
0 to under PCI0.
After that, all the PCI devices found their ACPI companion and the
firmware_node symlink is present and correct.
I2C-core creates a symlink for the attached device on the right controller.
/sys/bus/i2c/devices/i2c-24C02:00 ->
../../../devices/pci0000:00/0000:00:18.3/i2c-3/i2c-24C02:00
So that part is solved. (And I'll have to send a patch to coreboot...)

The next issue is that the I2C-core isn't matching the device to the
"at24" driver, which has the alias "24c02".

I used to instantiate the device from user space with:
# echo 24c02 0x57 > /sys/bus/i2c/devices/i2c-3/new_device
That now shows the address is busy, so it is creating the device, just
not linking it to the driver.

I'll dig further and see what I can see.

Thanks for your help.
Ben