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PTM requires an unbroken path of PTM-supporting devices between the PTM Root and the ultimate PTM Requester, but if a Switch supports PTM, only the Upstream Port can have a PTM Capability; the Downstream Ports do not. Previously we copied the PTM configuration from the Switch Upstream Port to the Downstream Ports so dev->ptm_enabled for any device implied that all the upstream devices support PTM. Instead of making it look like Downstream Ports have their own PTM config, add pci_upstream_ptm(), which returns the upstream device that has a PTM Capability (either a Root Port or a Switch Upstream Port). Link: https://lore.kernel.org/r/20220909202505.314195-3-helgaas@kernel.org Tested-by: Rajvi Jingar <rajvi.jingar@linux.intel.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>