Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value

Borislav Petkov
2020-08-02T20:18:47Z

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...

--
Regards/Gruss,
Boris.