task #29600094

commit 35a0b2378c199d4f26e458b2ca38ea56aaf2d9b8 upstream.
Backport summary: for 4.19 kernel ICX PCIe Gen4 support.

Prior to eed85ff4 ("PCI/DPC: Enable DPC only if AER is available"),
Linux handled DPC events regardless of whether firmware had granted it
ownership of AER or DPC, e.g., via _OSC.

PCIe r5.0, sec 6.2.10, recommends that the OS link control of DPC to
control of AER, so after eed85ff4, Linux handles DPC events only if it
has control of AER.

On platforms that do not grant OS control of AER via _OSC, Linux DPC
handling worked before eed85ff4 but not after.

To make Linux DPC handling work on those platforms the same way they did
before, add a "pcie_ports=dpc-native" kernel parameter that makes Linux
handle DPC events regardless of whether it has control of AER.

[bhelgaas: commit log, move pcie_ports_dpc_native to drivers/pci/]
Link: https://lore.kernel.org/r/20191023192205.97024-1-olof@lixom.netSigned-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

(cherry picked from commit 35a0b2378c199d4f26e458b2ca38ea56aaf2d9b8)
Signed-off-by: NEthan Zhao <haifeng.zhao@intel.com>
Signed-off-by: NArtie Ding <artie.ding@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>