On Sun, Aug 02, 2020 at 02:14:06PM -0500, Bjorn Helgaas wrote:
Wait, I'm not convinced yet. I know that if a PCI read fails, you normally get ~0 data because the host bridge fabricates it to complete the CPU load.
But what guarantees that a PCI config register cannot contain ~0?
Well, I don't think you can differentiate that case, right?
I guess this is where the driver knowledge comes into play: if the read returns ~0, the pci_read_config* should probably return in that case something like:
PCIBIOS_READ_MAYBE_FAILED
to denote it is all 1s and then the caller should be able to determine, based on any of domain:bus:slot.func and whatever else the driver knows about its hardware, whether the 1s are a valid value or an error. Hopefully.
Or something better of which I cannot think of right now...