PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller

This mostly reverts the commit b4c7d2076b4e ("PCI/LINK: Remove bandwidth
notification"). An upcoming commit extends this driver building PCIe
bandwidth controller on top of it.

PCIe bandwidth notifications were first added in the commit e8303bb7a75c
("PCI/LINK: Report degraded links via link bandwidth notification") but
later had to be removed. The significant changes compared with the old
bandwidth notification driver include:

1) Don't print the notifications into kernel log, just keep the Link
Speed cached in struct pci_bus updated. While somewhat unfortunate,
the log spam was the source of complaints that eventually lead to
the removal of the bandwidth notifications driver (see the links
below for further information).

2) Besides the Link Bandwidth Management Interrupt, also enable Link
Autonomous Bandwidth Interrupt to cover the other source of bandwidth
changes.

3) Handle Link Speed updates robustly. Refresh the cached Link Speed
when enabling Bandwidth Notification Interrupts, and solve the race
between Link Speed read and LBMS/LABS update in
pcie_bwnotif_irq_thread().

4) Use concurrency safe LNKCTL RMW operations.

5) The driver is now called PCIe bwctrl (bandwidth controller) instead
of just bandwidth notifications because of increased scope and
functionality within the driver.

6) Coexist with the Target Link Speed quirk in pcie_failed_link_retrain().
Provide LBMS counting API for it.

7) Tweaks to variable/functions names for consistency and length reasons.

Bandwidth Notifications enable the cur_bus_speed in the struct pci_bus to
keep track PCIe Link Speed changes.

[bhelgaas: This is based on previous work by Alexandru Gagniuc
<[e-mail]>; see e8303bb7a75c ("PCI/LINK: Report degraded links
via link bandwidth notification")]

Link: https://lore.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/all/[e-mail]/
Link: https://lore.kernel.org/linux-pci/[e-mail]/
Link: https://lore.kernel.org/linux-pci/[e-mail]/
Suggested-by: Lukas Wunner <[e-mail]> # Building bwctrl on top of bwnotif
Signed-off-by: Ilpo Järvinen <[e-mail]>
[bhelgaas: squash fix to drop IRQF_ONESHOT and convert to hardirq handler:
https://lore.kernel.org/r/[e-mail]]
Signed-off-by: Bjorn Helgaas <[e-mail]>
Tested-by: Stefan Wahren <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>

MAINTAINERS

···
 F:	include/linux/pci*
 F:	include/uapi/linux/pci*
 
+PCIE BANDWIDTH CONTROLLER
+M:	Ilpo Järvinen <[e-mail]>
+L:	[e-mail]
+S:	Supported
+F:	drivers/pci/pcie/bwctrl.c
+
 PCIE DRIVER FOR AMAZON ANNAPURNA LABS
 M:	Jonathan Chocron <[e-mail]>
 L:	[e-mail]

drivers/pci/hotplug/pciehp_ctrl.c

···
 #include <linux/types.h>
 #include <linux/pm_runtime.h>
 #include <linux/pci.h>
+
+#include "../pci.h"
 #include "pciehp.h"
 
 /* The following routines constitute the bulk of the
···
 
 	pciehp_set_indicators(ctrl, PCI_EXP_SLTCTL_PWR_IND_OFF,
 			      INDICATOR_NOOP);
+
+	/* Don't carry LBMS indications across */
+	pcie_reset_lbms_count(ctrl->pcie->port);
 }
 
 static int pciehp_enable_slot(struct controller *ctrl);

drivers/pci/pci.c

···
 	 * to track link speed or width changes made by hardware itself
 	 * in attempt to correct unreliable link operation.
 	 */
-	pcie_capability_write_word(pdev, PCI_EXP_LNKSTA, PCI_EXP_LNKSTA_LBMS);
+	pcie_reset_lbms_count(pdev);
 	return rc;
 }
 

drivers/pci/pci.h

···
 static inline void pcie_ecrc_get_policy(char *str) { }
 #endif
 
+#ifdef CONFIG_PCIEPORTBUS
+void pcie_reset_lbms_count(struct pci_dev *port);
+int pcie_lbms_count(struct pci_dev *port, unsigned long *val);
+#else
+static inline void pcie_reset_lbms_count(struct pci_dev *port) {}
+static inline int pcie_lbms_count(struct pci_dev *port, unsigned long *val)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 struct pci_dev_reset_methods {
 	u16 vendor;
 	u16 device;

drivers/pci/pcie/Makefile

···
 
 pcieportdrv-y			:= portdrv.o rcec.o
 
-obj-$(CONFIG_PCIEPORTBUS)	+= pcieportdrv.o
+obj-$(CONFIG_PCIEPORTBUS)	+= pcieportdrv.o bwctrl.o
 
 obj-y				+= aspm.o
 obj-$(CONFIG_PCIEAER)		+= aer.o err.o

drivers/pci/pcie/bwctrl.c

···
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * PCIe bandwidth controller
+ *
+ * Author: Alexandru Gagniuc <[e-mail]>
+ *
+ * Copyright (C) 2019 Dell Inc
+ * Copyright (C) 2023-2024 Intel Corporation
+ *
+ * This service port driver hooks into the Bandwidth Notification interrupt
+ * watching for changes or links becoming degraded in operation. It updates
+ * the cached Current Link Speed that is exposed to user space through sysfs.
+ */
+
+#define dev_fmt(fmt) "bwctrl: " fmt
+
+#include <linux/atomic.h>
+#include <linux/cleanup.h>
+#include <linux/errno.h>
+#include <linux/interrupt.h>
+#include <linux/pci.h>
+#include <linux/rwsem.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include "../pci.h"
+#include "portdrv.h"
+
+/**
+ * struct pcie_bwctrl_data - PCIe bandwidth controller
+ * @lbms_count:		Count for LBMS (since last reset)
+ */
+struct pcie_bwctrl_data {
+	atomic_t lbms_count;
+};
+
+/* Prevents port removal during LBMS count accessors */
+static DECLARE_RWSEM(pcie_bwctrl_lbms_rwsem);
+
+static void pcie_bwnotif_enable(struct pcie_device *srv)
+{
+	struct pcie_bwctrl_data *data = srv->port->link_bwctrl;
+	struct pci_dev *port = srv->port;
+	u16 link_status;
+	int ret;
+
+	/* Count LBMS seen so far as one */
+	ret = pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
+	if (ret == PCIBIOS_SUCCESSFUL && link_status & PCI_EXP_LNKSTA_LBMS)
+		atomic_inc(&data->lbms_count);
+
+	pcie_capability_set_word(port, PCI_EXP_LNKCTL,
+				 PCI_EXP_LNKCTL_LBMIE | PCI_EXP_LNKCTL_LABIE);
+	pcie_capability_write_word(port, PCI_EXP_LNKSTA,
+				   PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_LABS);
+
+	/*
+	 * Update after enabling notifications & clearing status bits ensures
+	 * link speed is up to date.
+	 */
+	pcie_update_link_speed(port->subordinate);
+}
+
+static void pcie_bwnotif_disable(struct pci_dev *port)
+{
+	pcie_capability_clear_word(port, PCI_EXP_LNKCTL,
+				   PCI_EXP_LNKCTL_LBMIE | PCI_EXP_LNKCTL_LABIE);
+}
+
+static irqreturn_t pcie_bwnotif_irq(int irq, void *context)
+{
+	struct pcie_device *srv = context;
+	struct pcie_bwctrl_data *data = srv->port->link_bwctrl;
+	struct pci_dev *port = srv->port;
+	u16 link_status, events;
+	int ret;
+
+	ret = pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
+	if (ret != PCIBIOS_SUCCESSFUL)
+		return IRQ_NONE;
+
+	events = link_status & (PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_LABS);
+	if (!events)
+		return IRQ_NONE;
+
+	if (events & PCI_EXP_LNKSTA_LBMS)
+		atomic_inc(&data->lbms_count);
+
+	pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
+
+	/*
+	 * Interrupts will not be triggered from any further Link Speed
+	 * change until LBMS is cleared by the write. Therefore, re-read the
+	 * speed (inside pcie_update_link_speed()) after LBMS has been
+	 * cleared to avoid missing link speed changes.
+	 */
+	pcie_update_link_speed(port->subordinate);
+
+	return IRQ_HANDLED;
+}
+
+void pcie_reset_lbms_count(struct pci_dev *port)
+{
+	struct pcie_bwctrl_data *data;
+
+	guard(rwsem_read)(&pcie_bwctrl_lbms_rwsem);
+	data = port->link_bwctrl;
+	if (data)
+		atomic_set(&data->lbms_count, 0);
+	else
+		pcie_capability_write_word(port, PCI_EXP_LNKSTA,
+					   PCI_EXP_LNKSTA_LBMS);
+}
+
+int pcie_lbms_count(struct pci_dev *port, unsigned long *val)
+{
+	struct pcie_bwctrl_data *data;
+
+	guard(rwsem_read)(&pcie_bwctrl_lbms_rwsem);
+	data = port->link_bwctrl;
+	if (!data)
+		return -ENOTTY;
+
+	*val = atomic_read(&data->lbms_count);
+
+	return 0;
+}
+
+static int pcie_bwnotif_probe(struct pcie_device *srv)
+{
+	struct pci_dev *port = srv->port;
+	int ret;
+
+	struct pcie_bwctrl_data *data = devm_kzalloc(&srv->device,
+						     sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	ret = devm_request_irq(&srv->device, srv->irq, pcie_bwnotif_irq,
+			       IRQF_SHARED, "PCIe bwctrl", srv);
+	if (ret)
+		return ret;
+
+	scoped_guard(rwsem_write, &pcie_bwctrl_lbms_rwsem) {
+		port->link_bwctrl = no_free_ptr(data);
+		pcie_bwnotif_enable(srv);
+	}
+
+	pci_dbg(port, "enabled with IRQ %d\n", srv->irq);
+
+	return 0;
+}
+
+static void pcie_bwnotif_remove(struct pcie_device *srv)
+{
+	pcie_bwnotif_disable(srv->port);
+	scoped_guard(rwsem_write, &pcie_bwctrl_lbms_rwsem)
+		srv->port->link_bwctrl = NULL;
+}
+
+static int pcie_bwnotif_suspend(struct pcie_device *srv)
+{
+	pcie_bwnotif_disable(srv->port);
+	return 0;
+}
+
+static int pcie_bwnotif_resume(struct pcie_device *srv)
+{
+	pcie_bwnotif_enable(srv);
+	return 0;
+}
+
+static struct pcie_port_service_driver pcie_bwctrl_driver = {
+	.name		= "pcie_bwctrl",
+	.port_type	= PCIE_ANY_PORT,
+	.service	= PCIE_PORT_SERVICE_BWCTRL,
+	.probe		= pcie_bwnotif_probe,
+	.suspend	= pcie_bwnotif_suspend,
+	.resume		= pcie_bwnotif_resume,
+	.remove		= pcie_bwnotif_remove,
+};
+
+int __init pcie_bwctrl_init(void)
+{
+	return pcie_port_service_register(&pcie_bwctrl_driver);
+}

drivers/pci/pcie/portdrv.c

···
 	 */
 
 	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP |
-		    PCIE_PORT_SERVICE_BWNOTIF)) {
+		    PCIE_PORT_SERVICE_BWCTRL)) {
 		pcie_capability_read_word(dev, PCI_EXP_FLAGS, &reg16);
 		*pme = FIELD_GET(PCI_EXP_FLAGS_IRQ, reg16);
 		nvec = *pme + 1;
···
 
 	/* 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_PORT_SERVICE_BWCTRL)) {
 		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;
+		irqs[PCIE_PORT_SERVICE_BWCTRL_SHIFT] = pcie_irq;
 	}
 
 	if (mask & PCIE_PORT_SERVICE_AER)
···
 
 		pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &linkcap);
 		if (linkcap & PCI_EXP_LNKCAP_LBNC)
-			services |= PCIE_PORT_SERVICE_BWNOTIF;
+			services |= PCIE_PORT_SERVICE_BWCTRL;
 	}
 
 	return services;
···
 	pcie_aer_init();
 	pcie_pme_init();
 	pcie_dpc_init();
+	pcie_bwctrl_init();
 	pcie_hp_init();
 }
 

drivers/pci/pcie/portdrv.h

···
 #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_SERVICE_BWCTRL_SHIFT	4	/* Bandwidth Controller (notifications) */
+#define PCIE_PORT_SERVICE_BWCTRL	(1 << PCIE_PORT_SERVICE_BWCTRL_SHIFT)
 
 #define PCIE_PORT_DEVICE_MAXSERVICES   5
 
···
 #else
 static inline int pcie_dpc_init(void) { return 0; }
 #endif
+
+int pcie_bwctrl_init(void);
 
 /* Port Type */
 #define PCIE_ANY_PORT			(~0)

drivers/pci/quirks.c

···
 
 static bool pcie_lbms_seen(struct pci_dev *dev, u16 lnksta)
 {
-	return lnksta & PCI_EXP_LNKSTA_LBMS;
+	unsigned long count;
+	int ret;
+
+	ret = pcie_lbms_count(dev, &count);
+	if (ret < 0)
+		return lnksta & PCI_EXP_LNKSTA_LBMS;
+
+	return count > 0;
 }
 
 /*

include/linux/pci.h

···
 };
 
 struct irq_affinity;
+struct pcie_bwctrl_data;
 struct pcie_link_state;
 struct pci_sriov;
 struct pci_p2pdma;
···
 	unsigned int	dpc_rp_extensions:1;
 	u8		dpc_rp_log_size;
 #endif
+	struct pcie_bwctrl_data		*link_bwctrl;
 #ifdef CONFIG_PCI_ATS
 	union {
 		struct pci_sriov	*sriov;		/* PF: SR-IOV info */