PCI: Workaround wrong flags completions for IDT switch

PCI: Workaround wrong flags completions for IDT switch

The IDT switch incorrectly flags an ACS source violation on a read config
request to an end point device on the completion (IDT 89H32H8G3-YC,
errata #36) even though the PCI Express spec states that completions are
never affected by ACS source violation (PCI Spec 3.1, Section 6.12.1.1).

The suggested workaround by IDT is to issue a configuration write to the
downstream device before issuing the first config read. This allows the
downstream device to capture its bus number, thus avoiding the ACS
violation on the completion.

The patch does the following -

1. Disable ACS source violation if enabled
2. Wait for config space access to become available by reading vendor id
3. Do a config write to the end point (errata workaround)
4. Enable ACS source validation (if it was enabled to begin with)

-v2: move workaround to pci_bus_read_dev_vendor_id() from
pci_bus_check_dev()
      and move enable_acs_sv to drivers/pci/pci.c -- by Yinghai
-v3: add bus->self check for root bus and virtual bus for sriov vfs.
-v4: only do workaround for IDT switches
-v5: tweak pci_std_enable_acs_sv to deal with unimplemented SV and
clarify return value

Signed-off-by: James Puthukattukaran <james.puthukattukaran@oracle.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
--

  drivers/pci/pci.c   | 37 +++++++++++++++++++++++++++++++++++++
  drivers/pci/pci.h   |  1 +
  drivers/pci/probe.c | 38 ++++++++++++++++++++++++++++++++++++--
  3 files changed, 74 insertions(+), 2 deletions(-)

Orabug: 26243152

Link: https://patchwork.kernel.org/patch/9828571/
Fixed wrapped lines in the original patch to fit the lines in 80 columns.
Changed variable types from integer to bool to keep consistent with function
return type.

Signed-off-by: Shan Hai <shan.hai@oracle.com>