Comment 123 for bug 1878279

I've been working with a Fedora reporter to try and solve the case where pci=nocrs helps to get a working touchpad, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1868899

Thanks to the latest set of logs attached there, I now am finally starting to understand what is going on here.

Your BIOS claims that any memory between 0x000000004bc50000-0x00000000cfffffff is reserved:

[ 0.000000] BIOS-e820: [mem 0x000000004bc50000-0x00000000cfffffff] reserved

But then continuous with placing the iomem window for PCI devices inside that reserved range:

[ 0.609988] pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]

This confuses the kernel and makes it unable to assign PCI iomem to devices which have not already been assigned iomem by the BIOS, like the I2C-controller used for the touchpad.

If you are interested in / curious about the low level details, I'm discussing this with the kernel PCI developers (including figuring out how to deal with this) here:
https://<email address hidden>/