linux-kernel - [PATCH v3 1/2] PCI: Initialize RCB from pci_configure

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Message-ID: <20260122130957.68757-2-haakon.bugge@oracle.com>
Date: Thu, 22 Jan 2026 14:09:53 +0100
From: Håkon Bugge <haakon.bugge@...cle.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>
Cc: Alex Williamson <alex@...zbot.org>,
        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 v3 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().

According to PCIe r7.0, sec 7.5.3.7, RCB is only valid for Root Ports
(where it is Read-Only), Bridges, and Endpoints. The bit is 'RsvdP'
for Virtual Functions. Hence, for other cases than Bridges and Physical
Endpoints, we bail out early from pci_configure_rcb().

If the Root Port's RCB cannot be determined, we do nothing.

If RCB is set in the Root Port and not in the device, we set it. If it
is set in the device but not in the Root Port, we print an info
message and reset 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.

v2 -> v3:
   * Qualified the device types more strictly
   * s/pcie_root_rcb_set/pcie_read_root_rcb/ and changed signature
   * Do nothing if the RP's RCB cannot be determined
   * Reset the device's RCB if not set in the RP
---
 drivers/pci/probe.c | 53 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 41183aed8f5d9..7165ac4065c97 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2410,6 +2410,58 @@ static void pci_configure_serr(struct pci_dev *dev)
 	}
 }
 
+static bool pcie_read_root_rcb(struct pci_dev *dev, bool *rcb)
+{
+	struct pci_dev *rp = pcie_find_root_port(dev);
+	u16 lnkctl;
+
+	if (!rp)
+		return false;
+
+	pcie_capability_read_word(rp, PCI_EXP_LNKCTL, &lnkctl);
+
+	*rcb = !!(lnkctl & PCI_EXP_LNKCTL_RCB);
+	return true;
+}
+
+static void pci_configure_rcb(struct pci_dev *dev)
+{
+	u16 lnkctl;
+	bool rcb;
+
+	/*
+	 * Per PCIe r7.0, sec 7.5.3.7, RCB is only meaningful in Root
+	 * Ports (where it is read-only), Endpoints, and Bridges.  It
+	 * may only be set for Endpoints and Bridges if it is set in
+	 * the Root Port. For Endpoints, it is 'RsvdP' for Virtual
+	 * Functions. If the Root Port's RCB cannot be determined, we
+	 * bail out.
+	 */
+	if (!pci_is_pcie(dev) ||
+	    pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
+	    pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM ||
+	    pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
+	    pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC ||
+	    dev->is_virtfn || !pcie_read_root_rcb(dev, &rcb))
+		return;
+
+	pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &lnkctl);
+	if (rcb) {
+		if (lnkctl & PCI_EXP_LNKCTL_RCB)
+			return;
+
+		lnkctl |= PCI_EXP_LNKCTL_RCB;
+	} else {
+		if (!(lnkctl & PCI_EXP_LNKCTL_RCB))
+			return;
+
+		pci_info(dev, FW_INFO "clearing RCB (RCB not set in Root Port)\n");
+		lnkctl &= ~PCI_EXP_LNKCTL_RCB;
+	}
+
+	pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnkctl);
+}
+
 static void pci_configure_device(struct pci_dev *dev)
 {
 	pci_configure_mps(dev);
@@ -2419,6 +2471,7 @@ 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