linux/drivers/pci/pcie/bwctrl.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * PCIe bandwidth controller
 *
 * Author: Alexandru Gagniuc <mr.nuke.me@gmail.com>
 *
 * Copyright (C) 2019 Dell Inc
 * Copyright (C) 2023-2024 Intel Corporation
 *
 * The PCIe bandwidth controller provides a way to alter PCIe Link Speeds
 * and notify the operating system when the Link Width or Speed changes. The
 * notification capability is required for all Root Ports and Downstream
 * Ports supporting Link Width wider than x1 and/or multiple Link Speeds.
 *
 * 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/bitops.h>
#include <linux/bits.h>
#include <linux/cleanup.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/mutex.h>
#include <linux/pci.h>
#include <linux/pci-bwctrl.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
 * @set_speed_mutex:	Serializes link speed changes
 * @lbms_count:		Count for LBMS (since last reset)
 * @cdev:		Thermal cooling device associated with the port
 */
struct pcie_bwctrl_data {
	struct mutex set_speed_mutex;
	atomic_t lbms_count;
	struct thermal_cooling_device *cdev;
};

/*
 * Prevent port removal during LBMS count accessors and Link Speed changes.
 *
 * These have to be differentiated because pcie_bwctrl_change_speed() calls
 * pcie_retrain_link() which uses LBMS count reset accessor on success
 * (using just one rwsem triggers "possible recursive locking detected"
 * warning).
 */
static DECLARE_RWSEM(pcie_bwctrl_lbms_rwsem);
static DECLARE_RWSEM(pcie_bwctrl_setspeed_rwsem);

static bool pcie_valid_speed(enum pci_bus_speed speed)
{
	return (speed >= PCIE_SPEED_2_5GT) && (speed <= PCIE_SPEED_64_0GT);
}

static u16 pci_bus_speed2lnkctl2(enum pci_bus_speed speed)
{
	static const u8 speed_conv[] = {
		[PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
		[PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
		[PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
		[PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
		[PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
		[PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
	};

	if (WARN_ON_ONCE(!pcie_valid_speed(speed)))
		return 0;

	return speed_conv[speed];
}

static inline u16 pcie_supported_speeds2target_speed(u8 supported_speeds)
{
	return __fls(supported_speeds);
}

/**
 * pcie_bwctrl_select_speed - Select Target Link Speed
 * @port:	PCIe Port
 * @speed_req:	Requested PCIe Link Speed
 *
 * Select Target Link Speed by take into account Supported Link Speeds of
 * both the Root Port and the Endpoint.
 *
 * Return: Target Link Speed (1=2.5GT/s, 2=5GT/s, 3=8GT/s, etc.)
 */
static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed speed_req)
{
	struct pci_bus *bus = port->subordinate;
	u8 desired_speeds, supported_speeds;
	struct pci_dev *dev;

	desired_speeds = GENMASK(pci_bus_speed2lnkctl2(speed_req),
				 __fls(PCI_EXP_LNKCAP2_SLS_2_5GB));

	supported_speeds = port->supported_speeds;
	if (bus) {
		down_read(&pci_bus_sem);
		dev = list_first_entry_or_null(&bus->devices, struct pci_dev, bus_list);
		if (dev)
			supported_speeds &= dev->supported_speeds;
		up_read(&pci_bus_sem);
	}
	if (!supported_speeds)
		supported_speeds = PCI_EXP_LNKCAP2_SLS_2_5GB;

	return pcie_supported_speeds2target_speed(supported_speeds & desired_speeds);
}

static int pcie_bwctrl_change_speed(struct pci_dev *port, u16 target_speed, bool use_lt)
{
	int ret;

	ret = pcie_capability_clear_and_set_word(port, PCI_EXP_LNKCTL2,
						 PCI_EXP_LNKCTL2_TLS, target_speed);
	if (ret != PCIBIOS_SUCCESSFUL)
		return pcibios_err_to_errno(ret);

	ret = pcie_retrain_link(port, use_lt);
	if (ret < 0)
		return ret;

	/*
	 * Ensure link speed updates also with platforms that have problems
	 * with notifications.
	 */
	if (port->subordinate)
		pcie_update_link_speed(port->subordinate);

	return 0;
}

/**
 * pcie_set_target_speed - Set downstream Link Speed for PCIe Port
 * @port:	PCIe Port
 * @speed_req:	Requested PCIe Link Speed
 * @use_lt:	Wait for the LT or DLLLA bit to detect the end of link training
 *
 * Attempt to set PCIe Port Link Speed to @speed_req. @speed_req may be
 * adjusted downwards to the best speed supported by both the Port and PCIe
 * Device underneath it.
 *
 * Return:
 * * 0		- on success
 * * -EINVAL	- @speed_req is not a PCIe Link Speed
 * * -ENODEV	- @port is not controllable
 * * -ETIMEDOUT	- changing Link Speed took too long
 * * -EAGAIN	- Link Speed was changed but @speed_req was not achieved
 */
int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
			  bool use_lt)
{
	struct pci_bus *bus = port->subordinate;
	u16 target_speed;
	int ret;

	if (WARN_ON_ONCE(!pcie_valid_speed(speed_req)))
		return -EINVAL;

	if (bus && bus->cur_bus_speed == speed_req)
		return 0;

	target_speed = pcie_bwctrl_select_speed(port, speed_req);

	scoped_guard(rwsem_read, &pcie_bwctrl_setspeed_rwsem) {
		struct pcie_bwctrl_data *data = port->link_bwctrl;

		/*
		 * port->link_bwctrl is NULL during initial scan when called
		 * e.g. from the Target Speed quirk.
		 */
		if (data)
			mutex_lock(&data->set_speed_mutex);

		ret = pcie_bwctrl_change_speed(port, target_speed, use_lt);

		if (data)
			mutex_unlock(&data->set_speed_mutex);
	}

	/*
	 * Despite setting higher speed into the Target Link Speed, empty
	 * bus won't train to 5GT+ speeds.
	 */
	if (!ret && bus && bus->cur_bus_speed != speed_req &&
	    !list_empty(&bus->devices))
		ret = -EAGAIN;

	return ret;
}

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;

	/* Can happen if we run out of bus numbers during enumeration. */
	if (!port->subordinate)
		return -ENODEV;

	struct pcie_bwctrl_data *data = devm_kzalloc(&srv->device,
						     sizeof(*data), GFP_KERNEL);
	if (!data)
		return -ENOMEM;

	ret = devm_mutex_init(&srv->device, &data->set_speed_mutex);
	if (ret)
		return ret;

	scoped_guard(rwsem_write, &pcie_bwctrl_setspeed_rwsem) {
		scoped_guard(rwsem_write, &pcie_bwctrl_lbms_rwsem) {
			port->link_bwctrl = data;

			ret = request_irq(srv->irq, pcie_bwnotif_irq,
					  IRQF_SHARED, "PCIe bwctrl", srv);
			if (ret) {
				port->link_bwctrl = NULL;
				return ret;
			}

			pcie_bwnotif_enable(srv);
		}
	}

	pci_dbg(port, "enabled with IRQ %d\n", srv->irq);

	/* Don't fail on errors. Don't leave IS_ERR() "pointer" into ->cdev */
	port->link_bwctrl->cdev = pcie_cooling_device_register(port);
	if (IS_ERR(port->link_bwctrl->cdev))
		port->link_bwctrl->cdev = NULL;

	return 0;
}

static void pcie_bwnotif_remove(struct pcie_device *srv)
{
	struct pcie_bwctrl_data *data = srv->port->link_bwctrl;

	pcie_cooling_device_unregister(data->cdev);

	scoped_guard(rwsem_write, &pcie_bwctrl_setspeed_rwsem) {
		scoped_guard(rwsem_write, &pcie_bwctrl_lbms_rwsem) {
			pcie_bwnotif_disable(srv->port);

			free_irq(srv->irq, srv);

			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);
}