[PATCH] PCI: Skip devices with RRS Vendor ID(0x0001) on root bus

[Zhu Lingshan <lingshan.zhu@amd.com>]

PCIe Request Retry Status (RRS) is a link-layer mechanism where a
downstream device responds with RRS to indicate it is not ready.

With RRS Software Visibility enabled, the Root Port translates
RRS into Vendor ID 0x0001 (reserved by PCI SIG) for the driver.

Devices on the root bus, for example the root port itself,
have no upstream PCIe link and can never legitimately return RRS.

This patch skips any devices with RRS Vendor ID 0x0001
on the root bus instead of entering the RRS retry loop.

Signed-off-by: Zhu Lingshan <lingshan.zhu@amd.com>
---
 drivers/pci/probe.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index bccc7a4bdd79..2fad89ca594c 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2578,8 +2578,27 @@ bool pci_bus_generic_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
 	    *l == 0x0000ffff || *l == 0xffff0000)
 		return false;
 
-	if (pci_bus_rrs_vendor_id(*l))
+	if (pci_bus_rrs_vendor_id(*l)) {
+		/*
+		 * RRS (Request Retry Status) is a PCIe link-layer mechanism
+		 * where a downstream device sends a RRS completion status, and the
+		 * Root Port (with RRS Software Visibility enabled) translates
+		 * it to Vendor ID 0x0001 for the driver, indicating the
+		 * device is not ready.
+		 *
+		 * Therefore, RRS is a root port feature, and devices on the root bus,
+		 * for example the root port itself have no upstream PCIe link,
+		 * so they can never legitimately return RRS.
+		 */
+		if (pci_is_root_bus(bus)) {
+			pr_err("pci %04x:%02x:%02x.%d: invalid Vendor ID %04x (RRS, reserved by PCI SIG) on root bus, buggy device\n",
+				pci_domain_nr(bus), bus->number,
+				PCI_SLOT(devfn), PCI_FUNC(devfn),
+				*l & 0xffff);
+			return false;
+		}
 		return pci_bus_wait_rrs(bus, devfn, l, timeout);
+	}
 
 	return true;
 }
-- 
2.53.0