[PATCH v7 6/8] PCI/bwctrl: Add API to set PCIe Link Speed

Ilpo Järvinen
2024-09-10T12:28:45Z

Currently, PCIe Link Speeds are adjusted by custom code rather than in
a common function provided in PCI core. PCIe bandwidth controller
(bwctrl) introduces an in-kernel API to set PCIe Link Speed.

Convert Target Speed quirk to use the new API. The Target Speed quirk
runs very early when bwctrl is not yet probed for a Port and can also
run later when bwctrl is already setup for the Port. Also, the new API
has to be available for the Target Speed quirk when bwctrl is not
enabled by the config. The cases when bwctrl is not setup for the port
use less locking which is handled by a few locking wrappers.

The new API is also intended to be used in an upcoming commit that adds
a thermal cooling device to throttle PCIe bandwidth when thermal
thresholds are reached.

The PCIe bandwidth control procedure is as follows. The highest speed
supported by the Port and the PCIe device which is not higher than the
requested speed is selected and written into the Target Link Speed in
the Link Control 2 Register. Then bandwidth controller retrains the
PCIe Link.

Bandwidth Notifications enable the cur_bus_speed in the struct pci_bus
to keep track PCIe Link Speed changes. While Bandwidth Notifications
should also be generated when bandwidth controller alters the PCIe Link
Speed, a few platforms do not deliver LMBS interrupt after Link
Training as expected. Thus, after changing the Link Speed, bandwidth
controller makes additional read for the Link Status Register to ensure
cur_bus_speed is consistent with the new PCIe Link Speed.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
drivers/pci/pci.h | 20 ++++
drivers/pci/pcie/Makefile | 2 +-
drivers/pci/pcie/bwctrl.c | 200 +++++++++++++++++++++++++++++++++++++-
drivers/pci/quirks.c | 17 +---
include/linux/pci.h | 3 +
5 files changed, 226 insertions(+), 16 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 869677ff752f..7f0e71f3ce67 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -313,6 +313,17 @@ void pci_disable_bridge_window(struct pci_dev *dev);
struct pci_bus *pci_bus_get(struct pci_bus *bus);
void pci_bus_put(struct pci_bus *bus);

+#define PCIE_LNKCAP_SLS2SPEED(lnkcap) \
+({ \
+ (lnkcap == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
+ lnkcap == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
+ lnkcap == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
+ lnkcap == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
+ lnkcap == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
+ lnkcap == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
+ PCI_SPEED_UNKNOWN); \
+})
+
/* PCIe link information from Link Capabilities 2 */
#define PCIE_LNKCAP2_SLS2SPEED(lnkcap2) \
((lnkcap2) & PCI_EXP_LNKCAP2_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
@@ -323,6 +334,15 @@ void pci_bus_put(struct pci_bus *bus);
(lnkcap2) & PCI_EXP_LNKCAP2_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
PCI_SPEED_UNKNOWN)

+#define PCIE_LNKCTL2_TLS2SPEED(lnkctl2) \
+ ((lnkctl2) == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT : \
+ (lnkctl2) == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT : \
+ (lnkctl2) == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT : \
+ (lnkctl2) == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT : \
+ (lnkctl2) == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT : \
+ (lnkctl2) == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
+ PCI_SPEED_UNKNOWN)
+
/* PCIe speed to Mb/s reduced by encoding overhead */
#define PCIE_SPEED2MBS_ENC(speed) \
((speed) == PCIE_SPEED_64_0GT ? 64000*1/1 : \
diff --git a/drivers/pci/pcie/Makefile b/drivers/pci/pcie/Makefile
index 6357bc219632..e8cf58a0fa3f 100644
--- a/drivers/pci/pcie/Makefile
+++ b/drivers/pci/pcie/Makefile
@@ -12,5 +12,5 @@ obj-$(CONFIG_PCIEAER_INJECT) += aer_inject.o
obj-$(CONFIG_PCIE_PME) += pme.o
obj-$(CONFIG_PCIE_DPC) += dpc.o
obj-$(CONFIG_PCIE_PTM) += ptm.o
-obj-$(CONFIG_PCIE_BWCTRL) += bwctrl.o
+obj-y += bwctrl.o
obj-$(CONFIG_PCIE_EDR) += edr.o
diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
index 1b11b5da79d4..cc245aaf8d5e 100644
--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -7,6 +7,11 @@
* 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.
@@ -15,9 +20,12 @@
#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/rwsem.h>
#include <linux/slab.h>
@@ -28,15 +36,198 @@

/**
* struct pcie_bwctrl_data - PCIe bandwidth controller
+ * @set_speed_mutex: Serializes link speed changes
* @lbms_count: Count for LBMS (since last reset)
*/
struct pcie_bwctrl_data {
+ struct mutex set_speed_mutex;
atomic_t lbms_count;
};

+#ifdef CONFIG_PCIE_BWCTRL
/* Prevents port removal during link speed changes and LBMS count accessors */
static DECLARE_RWSEM(pcie_bwctrl_remove_rwsem);

+static inline void pcie_bwctrl_remove_rwsem_down_read(void)
+{
+ down_read(&pcie_bwctrl_remove_rwsem);
+}
+
+static inline void pcie_bwctrl_remove_rwsem_up_read(void)
+{
+ up_read(&pcie_bwctrl_remove_rwsem);
+}
+
+static inline void pcie_bwctrl_port_mutex_lock(struct pci_dev *port)
+{
+ struct pcie_bwctrl_data *data;
+
+ /*
+ * port->link_bwctrl is NULL when Target Speed quirk runs during
+ * boot and when bwctrl is not enabled by the config.
+ */
+ data = port->link_bwctrl;
+ if (!data)
+ return;
+
+ mutex_lock(&data->set_speed_mutex);
+}
+
+static inline void pcie_bwctrl_port_mutex_unlock(struct pci_dev *port)
+{
+ struct pcie_bwctrl_data *data;
+
+ /*
+ * port->link_bwctrl is NULL when Target Speed quirk runs during
+ * boot and when bwctrl is not enabled by the config.
+ */
+ data = port->link_bwctrl;
+ if (!data)
+ return;
+
+ mutex_unlock(&data->set_speed_mutex);
+}
+#else
+static inline void pcie_bwctrl_remove_rwsem_down_read(void) {}
+static inline void pcie_bwctrl_remove_rwsem_up_read(void) {}
+static inline void pcie_bwctrl_port_mutex_lock(struct pci_dev *port) {}
+static inline void pcie_bwctrl_port_mutex_unlock(struct pci_dev *port) {}
+#endif /* CONFIG_PCIE_BWCTRL */
+
+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)
+ return 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
+ *
+ * Attempts 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);
+
+ pcie_bwctrl_remove_rwsem_down_read();
+ pcie_bwctrl_port_mutex_lock(port);
+ ret = pcie_bwctrl_change_speed(port, target_speed, use_lt);
+ pcie_bwctrl_port_mutex_unlock(port);
+ pcie_bwctrl_remove_rwsem_up_read();
+
+ /*
+ * 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;
+}
+EXPORT_SYMBOL_GPL(pcie_set_target_speed);
+
+#ifdef CONFIG_PCIE_BWCTRL
static void pcie_bwnotif_enable(struct pcie_device *srv)
{
struct pcie_bwctrl_data *data = get_service_data(srv);
@@ -135,6 +326,7 @@ static int pcie_bwnotif_probe(struct pcie_device *srv)
if (!data)
return -ENOMEM;

+ mutex_init(&data->set_speed_mutex);
set_service_data(srv, data);

ret = request_threaded_irq(srv->irq, NULL, pcie_bwnotif_irq_thread,
@@ -142,8 +334,10 @@ static int pcie_bwnotif_probe(struct pcie_device *srv)
if (ret)
return ret;

- port->link_bwctrl = no_free_ptr(data);
- pcie_bwnotif_enable(srv);
+ scoped_guard(rwsem_write, &pcie_bwctrl_remove_rwsem) {
+ port->link_bwctrl = no_free_ptr(data);
+ pcie_bwnotif_enable(srv);
+ }

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

@@ -159,6 +353,7 @@ static void pcie_bwnotif_remove(struct pcie_device *srv)
srv->port->link_bwctrl = NULL;

free_irq(srv->irq, srv);
+ mutex_destroy(&data->set_speed_mutex);
kfree(data);
}

@@ -188,3 +383,4 @@ int __init pcie_bwctrl_init(void)
{
return pcie_port_service_register(&pcie_bwctrl_driver);
}
+#endif /* CONFIG_PCIE_BWCTRL */
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 64d9f8559f65..3bca70da1d45 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -113,16 +113,11 @@ int pcie_failed_link_retrain(struct pci_dev *dev)

pci_info(dev, "broken device, retraining non-functional downstream link at 2.5GT/s\n");

- lnkctl2 &= ~PCI_EXP_LNKCTL2_TLS;
- lnkctl2 |= PCI_EXP_LNKCTL2_TLS_2_5GT;
- pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, lnkctl2);
-
- ret = pcie_retrain_link(dev, false);
+ ret = pcie_set_target_speed(dev, PCIE_SPEED_2_5GT, false);
if (ret) {
pci_info(dev, "retraining failed\n");
- pcie_capability_write_word(dev, PCI_EXP_LNKCTL2,
- oldlnkctl2);
- pcie_retrain_link(dev, true);
+ pcie_set_target_speed(dev, PCIE_LNKCTL2_TLS2SPEED(oldlnkctl2),
+ true);
return ret;
}

@@ -136,11 +131,7 @@ int pcie_failed_link_retrain(struct pci_dev *dev)

pci_info(dev, "removing 2.5GT/s downstream link speed restriction\n");
pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &lnkcap);
- lnkctl2 &= ~PCI_EXP_LNKCTL2_TLS;
- lnkctl2 |= lnkcap & PCI_EXP_LNKCAP_SLS;
- pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, lnkctl2);
-
- ret = pcie_retrain_link(dev, false);
+ ret = pcie_set_target_speed(dev, PCIE_LNKCAP_SLS2SPEED(lnkcap), false);
if (ret) {
pci_info(dev, "retraining failed\n");
return ret;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d77816f0193f..3af842e6346d 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1845,6 +1845,9 @@ bool pci_aer_available(void);
static inline bool pci_aer_available(void) { return false; }
#endif

+int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
+ bool use_lt);
+
bool pci_ats_disabled(void);

#ifdef CONFIG_PCIE_PTM
--
2.39.2