[PATCH] Revert "PCI/LINK: Report degraded links via link bandwidth notification"

[Bjorn Helgaas <helgaas@kernel.org>]

From: Bjorn Helgaas <bhelgaas@google.com>

This reverts commit e8303bb7a75c113388badcc49b2a84b4121c1b3e.

e8303bb7a75c added logging whenever a link changed speed or width to a
state that is considered degraded.  Unfortunately, it cannot differentiate
signal integrity-related link changes from those intentionally initiated by
an endpoint driver, including drivers that may live in userspace or VMs
when making use of vfio-pci.  Some GPU drivers actively manage the link
state to save power, which generates a stream of messages like this:

  vfio-pci 0000:07:00.0: 32.000 Gb/s available PCIe bandwidth, limited by 2.5 GT/s x16 link at 0000:00:02.0 (capable of 64.000 Gb/s with 5 GT/s x16 link)

We really *do* want to be alerted when the link bandwidth is reduced
because of hardware failures, but degradation by intentional link state
management is probably far more common, so the signal-to-noise ratio is
currently low.

Until we figure out a way to identify the real problems or silence the
intentional situations, revert the following commits, which include the
initial implementation (e8303bb7a75c) and subsequent fixes:

    e8303bb7a75c ("PCI/LINK: Report degraded links via link bandwidth notification")
    3e82a7f9031f ("PCI/LINK: Supply IRQ handler so level-triggered IRQs are acked")
    55397ce8df48 ("PCI/LINK: Clear bandwidth notification interrupt before enabling it")
    0fa635aec9ab ("PCI/LINK: Deduplicate bandwidth reports for multi-function devices")

Link: https://lore.kernel.org/lkml/155597243666.19387.1205950870601742062.stgit@gimli.home
Link: https://lore.kernel.org/lkml/155605909349.3575.13433421148215616375.stgit@gimli.home
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Alexandru Gagniuc <mr.nuke.me@gmail.com>
CC: Lukas Wunner <lukas@wunner.de>
CC: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/pci/pci.h                  |   1 -
 drivers/pci/pcie/Makefile          |   1 -
 drivers/pci/pcie/bw_notification.c | 121 -----------------------------
 drivers/pci/pcie/portdrv.h         |   6 +-
 drivers/pci/pcie/portdrv_core.c    |  17 ++--
 drivers/pci/pcie/portdrv_pci.c     |   1 -
 drivers/pci/probe.c                |   2 +-
 7 files changed, 7 insertions(+), 142 deletions(-)
 delete mode 100644 drivers/pci/pcie/bw_notification.c

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index d994839a3e24..224d88634115 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -273,7 +273,6 @@ enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev);
 u32 pcie_bandwidth_capable(struct pci_dev *dev, enum pci_bus_speed *speed,
 			   enum pcie_link_width *width);
 void __pcie_print_link_status(struct pci_dev *dev, bool verbose);
-void pcie_report_downtraining(struct pci_dev *dev);
 
 /* Single Root I/O Virtualization */
 struct pci_sriov {
diff --git a/drivers/pci/pcie/Makefile b/drivers/pci/pcie/Makefile
index f1d7bc1e5efa..ab514083d5d4 100644
--- a/drivers/pci/pcie/Makefile
+++ b/drivers/pci/pcie/Makefile
@@ -3,7 +3,6 @@
 # Makefile for PCI Express features and port driver
 
 pcieportdrv-y			:= portdrv_core.o portdrv_pci.o err.o
-pcieportdrv-y			+= bw_notification.o
 
 obj-$(CONFIG_PCIEPORTBUS)	+= pcieportdrv.o
 
diff --git a/drivers/pci/pcie/bw_notification.c b/drivers/pci/pcie/bw_notification.c
deleted file mode 100644
index 4fa9e3523ee1..000000000000
--- a/drivers/pci/pcie/bw_notification.c
+++ /dev/null
@@ -1,121 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0+
-/*
- * PCI Express Link Bandwidth Notification services driver
- * Author: Alexandru Gagniuc <mr.nuke.me@gmail.com>
- *
- * Copyright (C) 2019, Dell Inc
- *
- * The PCIe Link Bandwidth Notification provides a way to notify the
- * operating system when the link width or data rate changes.  This
- * capability is required for all root ports and downstream ports
- * supporting links wider than x1 and/or multiple link speeds.
- *
- * This service port driver hooks into the bandwidth notification interrupt
- * and warns when links become degraded in operation.
- */
-
-#include "../pci.h"
-#include "portdrv.h"
-
-static bool pcie_link_bandwidth_notification_supported(struct pci_dev *dev)
-{
-	int ret;
-	u32 lnk_cap;
-
-	ret = pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &lnk_cap);
-	return (ret == PCIBIOS_SUCCESSFUL) && (lnk_cap & PCI_EXP_LNKCAP_LBNC);
-}
-
-static void pcie_enable_link_bandwidth_notification(struct pci_dev *dev)
-{
-	u16 lnk_ctl;
-
-	pcie_capability_write_word(dev, PCI_EXP_LNKSTA, PCI_EXP_LNKSTA_LBMS);
-
-	pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &lnk_ctl);
-	lnk_ctl |= PCI_EXP_LNKCTL_LBMIE;
-	pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnk_ctl);
-}
-
-static void pcie_disable_link_bandwidth_notification(struct pci_dev *dev)
-{
-	u16 lnk_ctl;
-
-	pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &lnk_ctl);
-	lnk_ctl &= ~PCI_EXP_LNKCTL_LBMIE;
-	pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnk_ctl);
-}
-
-static irqreturn_t pcie_bw_notification_irq(int irq, void *context)
-{
-	struct pcie_device *srv = context;
-	struct pci_dev *port = srv->port;
-	u16 link_status, events;
-	int ret;
-
-	ret = pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
-	events = link_status & PCI_EXP_LNKSTA_LBMS;
-
-	if (ret != PCIBIOS_SUCCESSFUL || !events)
-		return IRQ_NONE;
-
-	pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
-	pcie_update_link_speed(port->subordinate, link_status);
-	return IRQ_WAKE_THREAD;
-}
-
-static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
-{
-	struct pcie_device *srv = context;
-	struct pci_dev *port = srv->port;
-	struct pci_dev *dev;
-
-	/*
-	 * Print status from downstream devices, not this root port or
-	 * downstream switch port.
-	 */
-	down_read(&pci_bus_sem);
-	list_for_each_entry(dev, &port->subordinate->devices, bus_list)
-		pcie_report_downtraining(dev);
-	up_read(&pci_bus_sem);
-
-	return IRQ_HANDLED;
-}
-
-static int pcie_bandwidth_notification_probe(struct pcie_device *srv)
-{
-	int ret;
-
-	/* Single-width or single-speed ports do not have to support this. */
-	if (!pcie_link_bandwidth_notification_supported(srv->port))
-		return -ENODEV;
-
-	ret = request_threaded_irq(srv->irq, pcie_bw_notification_irq,
-				   pcie_bw_notification_handler,
-				   IRQF_SHARED, "PCIe BW notif", srv);
-	if (ret)
-		return ret;
-
-	pcie_enable_link_bandwidth_notification(srv->port);
-
-	return 0;
-}
-
-static void pcie_bandwidth_notification_remove(struct pcie_device *srv)
-{
-	pcie_disable_link_bandwidth_notification(srv->port);
-	free_irq(srv->irq, srv);
-}
-
-static struct pcie_port_service_driver pcie_bandwidth_notification_driver = {
-	.name		= "pcie_bw_notification",
-	.port_type	= PCIE_ANY_PORT,
-	.service	= PCIE_PORT_SERVICE_BWNOTIF,
-	.probe		= pcie_bandwidth_notification_probe,
-	.remove		= pcie_bandwidth_notification_remove,
-};
-
-int __init pcie_bandwidth_notification_init(void)
-{
-	return pcie_port_service_register(&pcie_bandwidth_notification_driver);
-}
diff --git a/drivers/pci/pcie/portdrv.h b/drivers/pci/pcie/portdrv.h
index 1d50dc58ac40..fbbf00b0992e 100644
--- a/drivers/pci/pcie/portdrv.h
+++ b/drivers/pci/pcie/portdrv.h
@@ -20,10 +20,8 @@
 #define PCIE_PORT_SERVICE_HP		(1 << PCIE_PORT_SERVICE_HP_SHIFT)
 #define PCIE_PORT_SERVICE_DPC_SHIFT	3	/* Downstream Port Containment */
 #define PCIE_PORT_SERVICE_DPC		(1 << PCIE_PORT_SERVICE_DPC_SHIFT)
-#define PCIE_PORT_SERVICE_BWNOTIF_SHIFT	4	/* Bandwidth notification */
-#define PCIE_PORT_SERVICE_BWNOTIF	(1 << PCIE_PORT_SERVICE_BWNOTIF_SHIFT)
 
-#define PCIE_PORT_DEVICE_MAXSERVICES   5
+#define PCIE_PORT_DEVICE_MAXSERVICES   4
 
 #ifdef CONFIG_PCIEAER
 int pcie_aer_init(void);
@@ -49,8 +47,6 @@ int pcie_dpc_init(void);
 static inline int pcie_dpc_init(void) { return 0; }
 #endif
 
-int pcie_bandwidth_notification_init(void);
-
 /* Port Type */
 #define PCIE_ANY_PORT			(~0)
 
diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
index 7d04f9d087a6..f458ac9cb70c 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -99,7 +99,7 @@ static int pcie_message_numbers(struct pci_dev *dev, int mask,
  */
 static int pcie_port_enable_irq_vec(struct pci_dev *dev, int *irqs, int mask)
 {
-	int nr_entries, nvec, pcie_irq;
+	int nr_entries, nvec;
 	u32 pme = 0, aer = 0, dpc = 0;
 
 	/* Allocate the maximum possible number of MSI/MSI-X vectors */
@@ -135,13 +135,10 @@ static int pcie_port_enable_irq_vec(struct pci_dev *dev, int *irqs, int mask)
 			return nr_entries;
 	}
 
-	/* PME, hotplug and bandwidth notification share an MSI/MSI-X vector */
-	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP |
-		    PCIE_PORT_SERVICE_BWNOTIF)) {
-		pcie_irq = pci_irq_vector(dev, pme);
-		irqs[PCIE_PORT_SERVICE_PME_SHIFT] = pcie_irq;
-		irqs[PCIE_PORT_SERVICE_HP_SHIFT] = pcie_irq;
-		irqs[PCIE_PORT_SERVICE_BWNOTIF_SHIFT] = pcie_irq;
+	/* PME and hotplug share an MSI/MSI-X vector */
+	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP)) {
+		irqs[PCIE_PORT_SERVICE_PME_SHIFT] = pci_irq_vector(dev, pme);
+		irqs[PCIE_PORT_SERVICE_HP_SHIFT] = pci_irq_vector(dev, pme);
 	}
 
 	if (mask & PCIE_PORT_SERVICE_AER)
@@ -253,10 +250,6 @@ static int get_port_device_capability(struct pci_dev *dev)
 	    pci_aer_available() && services & PCIE_PORT_SERVICE_AER)
 		services |= PCIE_PORT_SERVICE_DPC;
 
-	if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
-	    pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
-		services |= PCIE_PORT_SERVICE_BWNOTIF;
-
 	return services;
 }
 
diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
index 0a87091a0800..99d2abe88d0b 100644
--- a/drivers/pci/pcie/portdrv_pci.c
+++ b/drivers/pci/pcie/portdrv_pci.c
@@ -240,7 +240,6 @@ static void __init pcie_init_services(void)
 	pcie_pme_init();
 	pcie_dpc_init();
 	pcie_hp_init();
-	pcie_bandwidth_notification_init();
 }
 
 static int __init pcie_portdrv_init(void)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 7e12d0163863..2ec0df04e0dc 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2388,7 +2388,7 @@ static struct pci_dev *pci_scan_device(struct pci_bus *bus, int devfn)
 	return dev;
 }
 
-void pcie_report_downtraining(struct pci_dev *dev)
+static void pcie_report_downtraining(struct pci_dev *dev)
 {
 	if (!pci_is_pcie(dev))
 		return;
-- 
2.21.0.593.g511ec345e18-goog