linux-kernel - [PATCH v2 1/2] PCI: Initialize RCB from pci_configure

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Message-ID: <20260121113544.4163457-2-haakon.bugge@oracle.com>
Date: Wed, 21 Jan 2026 12:35:40 +0100
From: Håkon Bugge <haakon.bugge@...cle.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Johannes Thumshirn <morbidrsa@...il.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Håkon Bugge <haakon.bugge@...cle.com>
Subject: [PATCH v2 1/2] PCI: Initialize RCB from pci_configure_device

Commit e42010d8207f ("PCI: Set Read Completion Boundary to 128 iff
Root Port supports it (_HPX)") fixed a bogus _HPX type 2 record, which
instructed program_hpx_type2() to set the RCB in an endpoint,
although it's RC did not have the RCB bit set.

e42010d8207f fixed that by qualifying the setting of the RCB in the
endpoint with the RC supporting an 128 byte RCB.

In retrospect, the program_hpx_type2() should only modify the AER
bits, and stay away from fiddling with the Link Control Register.

Hence, we explicitly program the RCB from pci_configure_device(). RCB
is RO in Root Ports, and in VFs, the bit is RsvdP, so for these two
cases we skip programming it. Then, if the Root Port has RCB set and
it is not set in the EP, we set it.

Fixes: Commit e42010d8207f ("PCI: Set Read Completion Boundary to 128 iff Root Port supports it (_HPX)")
Signed-off-by: Håkon Bugge <haakon.bugge@...cle.com>

---

Note, that the current duplication of pcie_root_rcb_set() will be
removed in the next commit.
---
 drivers/pci/probe.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 41183aed8f5d9..347af29868124 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2410,6 +2410,41 @@ static void pci_configure_serr(struct pci_dev *dev)
 	}
 }
 
+static bool pcie_root_rcb_set(struct pci_dev *dev)
+{
+	struct pci_dev *rp = pcie_find_root_port(dev);
+	u16 lnkctl;
+
+	if (!rp)
+		return false;
+
+	pcie_capability_read_word(rp, PCI_EXP_LNKCTL, &lnkctl);
+
+	return !!(lnkctl & PCI_EXP_LNKCTL_RCB);
+}
+
+static void pci_configure_rcb(struct pci_dev *dev)
+{
+	/*
+	 * Obviously, we need a Link Control register. The RCB is RO
+	 * in Root Ports, so no need to attempt to set it for
+	 * them. For VFs, the RCB is RsvdP, so, no need to set it.
+	 * Then, if the Root Port has RCB set, then we set for the EP
+	 * unless already set.
+	 */
+	if (pcie_cap_has_lnkctl(dev) &&
+	    (pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) &&
+	    !dev->is_virtfn && pcie_root_rcb_set(dev)) {
+		u16 lnkctl;
+
+		pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &lnkctl);
+		if (lnkctl & PCI_EXP_LNKCTL_RCB)
+			return;
+
+		pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnkctl | PCI_EXP_LNKCTL_RCB);
+	}
+}
+
 static void pci_configure_device(struct pci_dev *dev)
 {
 	pci_configure_mps(dev);
@@ -2419,6 +2454,7 @@ static void pci_configure_device(struct pci_dev *dev)
 	pci_configure_aspm_l1ss(dev);
 	pci_configure_eetlp_prefix(dev);
 	pci_configure_serr(dev);
+	pci_configure_rcb(dev);
 
 	pci_acpi_program_hp_params(dev);
 }
-- 
2.43.5