On Tue, 2020-07-14 at 13:45 -0500, Bjorn Helgaas wrote:

quoted

fail for valid arguments on a valid pci_device* ?

I really like this idea.

pci_write_config_*() has one return value, and only 100ish of 2500
callers check for errors.  It's sometimes possible for config
accessors to detect PCI errors and return failure, e.g., device was
removed or didn't respond, but most of them don't, and detecting
these
errors is not really that valuable.

pci_read_config_*() is much more interesting because it returns two
things, the function return value and the value read from the PCI
device, and it's complicated to check both. 

  .../...

I agree. It's a mess at the moment.

We have separate mechanism to convey PCI errors (among other things the
channel state) which should apply to config space when detection is
possible.

I think returning all 1's is the right thing to do here and avoids odd
duplicate error detection logic which I bet you is never properly
tested.

quoted

For b), it might be nice to also change other aspects of the
interface, e.g. passing a pci_host_bridge pointer plus bus number
instead of a pci_bus pointer, or having the callback in the
pci_host_bridge structure.

I like this idea a lot, too.  I think the fact that
pci_bus_read_config_word() requires a pci_bus * complicates things in
a few places.

I think it's completely separate, as you say, and we should defer it
for now because even part a) is a lot of work.  I added it to my list
of possible future projects.

Agreed on both points.

Cheers,
Ben.