linux-kernel - [PATCH] PCI: pciehp: Report degraded links via link bandwidth notification

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Date:   Wed, 28 Nov 2018 18:08:24 -0600
From:   Alexandru Gagniuc <mr.nuke.me@...il.com>
To:     bhelgaas@...gle.com
Cc:     austin_bolen@...l.com, alex_gagniuc@...lteam.com,
        keith.busch@...el.com, Shyam_Iyer@...l.com, lukas@...ner.de,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] PCI: pciehp: Report degraded links via link bandwidth notification

A warning is generated when a PCIe device is probed with a degraded
link, but there was no similar mechanism to warn when the link becomes
degraded after probing. The Link Bandwidth Notification provides this
mechanism.

Use the link bandwidth notification interrupt to detect bandwidth
changes, and rescan the bandwidth, looking for the weakest point. This
is the same logic used in probe().

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
---
 drivers/pci/hotplug/pciehp_hpc.c | 35 +++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 7dd443aea5a5..834672000b59 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -515,7 +515,8 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
 	struct controller *ctrl = (struct controller *)dev_id;
 	struct pci_dev *pdev = ctrl_dev(ctrl);
 	struct device *parent = pdev->dev.parent;
-	u16 status, events;
+	struct pci_dev *endpoint;
+	u16 status, events, link_status;
 
 	/*
 	 * Interrupts only occur in D3hot or shallower and only if enabled
@@ -525,6 +526,17 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
 	    (!(ctrl->slot_ctrl & PCI_EXP_SLTCTL_HPIE) && !pciehp_poll_mode))
 		return IRQ_NONE;
 
+	pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &link_status);
+
+	if (link_status & PCI_EXP_LNKSTA_LBMS) {
+		if (pdev->subordinate && pdev->subordinate->self)
+			endpoint = pdev->subordinate->self;
+		else
+			endpoint = pdev;
+		__pcie_print_link_status(endpoint, false);
+		pcie_capability_write_word(pdev, PCI_EXP_LNKSTA, link_status);
+	}
+
 	/*
 	 * Keep the port accessible by holding a runtime PM ref on its parent.
 	 * Defer resume of the parent to the IRQ thread if it's suspended.
@@ -677,6 +689,24 @@ static int pciehp_poll(void *data)
 	return 0;
 }
 
+static bool pcie_link_bandwidth_notification_supported(struct controller *ctrl)
+{
+	int ret;
+	u32 cap;
+
+	ret = pcie_capability_read_dword(ctrl_dev(ctrl), PCI_EXP_LNKCAP, &cap);
+	return (ret == PCIBIOS_SUCCESSFUL) && (cap & PCI_EXP_LNKCAP_LBNC);
+}
+
+static void pcie_enable_link_bandwidth_notification(struct controller *ctrl)
+{
+	u16 lnk_ctl;
+
+	pcie_capability_read_word(ctrl_dev(ctrl), PCI_EXP_LNKCTL, &lnk_ctl);
+	lnk_ctl |= PCI_EXP_LNKCTL_LBMIE;
+	pcie_capability_write_word(ctrl_dev(ctrl), PCI_EXP_LNKCTL, lnk_ctl);
+}
+
 static void pcie_enable_notification(struct controller *ctrl)
 {
 	u16 cmd, mask;
@@ -713,6 +743,9 @@ static void pcie_enable_notification(struct controller *ctrl)
 	pcie_write_cmd_nowait(ctrl, cmd, mask);
 	ctrl_dbg(ctrl, "%s: SLOTCTRL %x write cmd %x\n", __func__,
 		 pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, cmd);
+
+	if (pcie_link_bandwidth_notification_supported(ctrl))
+		pcie_enable_link_bandwidth_notification(ctrl);
 }
 
 static void pcie_disable_notification(struct controller *ctrl)
-- 
2.17.1