linux-kernel - [PATCH v2 2/2] PCI: AtomicOps: Fix logic in enable function

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Message-Id: <20251216-fix_pciatops-v2-2-d013e9b7e2ee@linux.ibm.com>
Date: Tue, 16 Dec 2025 18:04:43 +0100
From: Gerd Bayer <gbayer@...ux.ibm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>, Jay Cornwall <Jay.Cornwall@....com>,
        Felix Kuehling <Felix.Kuehling@....com>
Cc: Niklas Schnelle <schnelle@...ux.ibm.com>,
        Alexander Schmidt <alexs@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gerd Bayer <gbayer@...ux.ibm.com>, stable@...r.kernel.org
Subject: [PATCH v2 2/2] PCI: AtomicOps: Fix logic in enable function

Move the check for root port requirements past the loop within
pci_enable_atomic_ops_to_root() that checks on potential switch
(up- and downstream) ports.

Inside the loop traversing the PCI tree upwards, prepend the switch case
to validate the routing capability on any port with a fallthrough-case
that does the additional check for Atomic Ops not being blocked on
upstream ports.

Do not enable Atomic Op Requests if nothing can be learned about how the
device is attached - e.g. if it is on an "isolated" bus, as in s390.

Reported-by: Alexander Schmidt <alexs@...ux.ibm.com>
Cc: stable@...r.kernel.org
Fixes: 430a23689dea ("PCI: Add pci_enable_atomic_ops_to_root()")
Signed-off-by: Gerd Bayer <gbayer@...ux.ibm.com>
---
 drivers/pci/pci.c | 30 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index d2261ac964316f3fc3efc4d5b30cf821ac46d75d..5d25d42eece1bbaf16197068d7b6206937e9c3a0 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3675,7 +3675,7 @@ void pci_acs_init(struct pci_dev *dev)
 int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
 {
 	struct pci_bus *bus = dev->bus;
-	struct pci_dev *bridge;
+	struct pci_dev *bridge = NULL;
 	u32 cap, ctl2;
 
 	/*
@@ -3713,29 +3713,27 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
 		switch (pci_pcie_type(bridge)) {
 		/* Ensure switch ports support AtomicOp routing */
 		case PCI_EXP_TYPE_UPSTREAM:
-		case PCI_EXP_TYPE_DOWNSTREAM:
-			if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
-				return -EINVAL;
-			break;
-
-		/* Ensure root port supports all the sizes we care about */
-		case PCI_EXP_TYPE_ROOT_PORT:
-			if ((cap & cap_mask) != cap_mask)
-				return -EINVAL;
-			break;
-		}
-
-		/* Ensure upstream ports don't block AtomicOps on egress */
-		if (pci_pcie_type(bridge) == PCI_EXP_TYPE_UPSTREAM) {
+			/* Upstream ports must not block AtomicOps on egress */
 			pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2,
 						   &ctl2);
 			if (ctl2 & PCI_EXP_DEVCTL2_ATOMIC_EGRESS_BLOCK)
 				return -EINVAL;
+			fallthrough;
+		/* All switch ports need to route AtomicOps */
+		case PCI_EXP_TYPE_DOWNSTREAM:
+			if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
+				return -EINVAL;
+			break;
 		}
-
 		bus = bus->parent;
 	}
 
+	/* Finally, last bridge must be root port and support requested sizes */
+	if ((!bridge) ||
+	    (pci_pcie_type(bridge) != PCI_EXP_TYPE_ROOT_PORT) ||
+	    ((cap & cap_mask) != cap_mask))
+		return -EINVAL;
+
 	pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
 				 PCI_EXP_DEVCTL2_ATOMIC_REQ);
 	return 0;

-- 
2.51.0