On Thu, Nov 18, 2021 at 07:33:10PM +0530, Naveen Naidu wrote:

An MMIO read from a PCI device that doesn't exist or doesn't respond
causes a PCI error.  There's no real data to return to satisfy the 
CPU read, so most hardware fabricates ~0 data.

This patch series adds PCI_ERROR_RESPONSE definition and other helper
definition PCI_SET_ERROR_RESPONSE and PCI_POSSIBLE_ERROR and uses it
where appropriate to make these checks consistent and easier to find.

This helps unify PCI error response checking and make error check
consistent and easier to find.

This series also ensures that the error response fabrication now happens
in the PCI_OP_READ and PCI_USER_READ_CONFIG. This removes the
responsibility from controller drivers to do the error response setting. 

Applied to pci/error for v5.17.  Thanks, this is really nice work.
Somehow small changes like these add up to something much greater than
one would expect.

This touches many native controller drivers but in trivial ways, so I
plan to merge this branch after the usual native controller stuff from
Lorenzo.

I tweaked the commit logs to clarify that this series is all about
*config* reads, not MMIO reads.  MMIO reads have similar issues, and
we can use PCI_ERROR_RESPONSE, etc., there, too, but that's not what
this series does.

Bjorn