PCI/TPH: Allow TPH enable for RCiEPs

[ Upstream commit d3e996a ]

Previously, pcie_enable_tph() only enabled TLP Processing Hints (TPH) if
both the Endpoint and its Root Port advertised TPH support.

Root Complex Integrated Endpoints (RCiEPs) are directly integrated into a
Root Complex and do not have an associated Root Port, so pcie_enable_tph()
never enabled TPH for RCiEPs.

PCIe r7.0 doesn't seem to include a way to learn whether a Root Complex
supports TPH, but sec 2.2.7.1.1 says Functions that lack TPH support should
ignore TPH, and maybe the same is true for Root Complexes:

  A Function that does not support the TPH Completer or Routing capability
  and receives a transaction with the TH bit [which indicates the presence
  of TPH in the TLP header] Set is required to ignore the TH bit and handle
  the Request in the same way as Requests of the same transaction type
  without the TH bit Set.

Allow drivers to enable TPH for any RCiEP with a TPH Requester Capability.

Fixes: f69767a ("PCI: Add TLP Processing Hints (TPH) support")
Signed-off-by: George Abraham P <george.abraham.p@intel.com>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260109052923.1170070-1-george.abraham.p@intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: georgeabp

drivers/pci/tph.c

@@ -397,10 +397,13 @@ int pcie_enable_tph(struct pci_dev *pdev, int mode)
 	else
 		pdev->tph_req_type = PCI_TPH_REQ_TPH_ONLY;
 
-	rp_req_type = get_rp_completer_type(pdev);
+	/* Check if the device is behind a Root Port */
+	if (pci_pcie_type(pdev) != PCI_EXP_TYPE_RC_END) {
+		rp_req_type = get_rp_completer_type(pdev);
 
-	/* Final req_type is the smallest value of two */
-	pdev->tph_req_type = min(pdev->tph_req_type, rp_req_type);
+		/* Final req_type is the smallest value of two */
+		pdev->tph_req_type = min(pdev->tph_req_type, rp_req_type);
+	}
 
 	if (pdev->tph_req_type == PCI_TPH_REQ_DISABLE)
 		return -EINVAL;