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PCIe Link Retraining can alter Link Speed. pcie_retrain_link() that
performs the Link Training is called from bwctrl and ASPM driver.
While bwctrl listens for Link Bandwidth Management Status (LBMS) to
pick up changes in Link Speed, there is a race between
pcie_reset_lbms() clearing LBMS after the Link Training and
pcie_bwnotif_irq() reading the Link Status register. If LBMS is already
cleared when the irq handler reads the register, the interrupt handler
will return early with IRQ_NONE and won't update the Link Speed.
When Link Speed update originates from bwctrl,
pcie_bwctrl_change_speed() ensures Link Speed is updated after the
retraining. ASPM driver, however, calls pcie_retrain_link() but does
not update the Link Speed after retraining which can result in stale
Link Speed. Also, it is possible to have ASPM support with
CONFIG_PCIEPORTBUS=n in which case bwctrl will not be built in (and
thus won't update the Link Speed at all).
To ensure Link Speed is not left stale after Link Training, move the
call to pcie_update_link_speed() from pcie_bwctrl_change_speed() into
pcie_retrain_link().
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/linux-pci/aBCjpfyYmlkJ12AZ@wunner.de
Link: https://lore.kernel.org/r/20250514132821.15705-1-ilpo.jarvinen@linux.intel.com
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PCIe BW controller counted LBMS assertions for the purposes of the Target
Speed quirk (pcie_failed_link_retrain()). It was also a plan to expose the
LBMS count through sysfs to allow better diagnosing link related issues.
Lukas Wunner suggested, however, that adding a trace event would be better
for diagnostics purposes, leaving only pcie_failed_link_retrain() as a user
of the lbms_count.
The logic in pcie_failed_link_retrain() does not require keeping count of
LBMS assertions, so replace lbms_count with a simple flag in pci_dev's
priv_flags. The reduced complexity allows removing pcie_bwctrl_lbms_rwsem.
Since pcie_failed_link_retrain() runs before bwctrl is probed during boot,
the LBMS in Link Status register still has to be checked by the quirk.
The priv_flags numbering is not continuous because hotplug code added a few
flags to fill numbers 4-5 (hotplug and bwctrl changes are routed through in
different branches).
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
[kwilczynski: squashed a fix to resolve build failures from
https://lore.kernel.org/all/20250508090036.1528-1-ilpo.jarvinen@linux.intel.com]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Link: https://patch.msgid.link/20250422115548.1483-1-ilpo.jarvinen@linux.intel.com
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When BIOS neglects to assign bus numbers to PCI bridges, the kernel
attempts to correct that during PCI device enumeration. If it runs out
of bus numbers, no pci_bus is allocated and the "subordinate" pointer in
the bridge's pci_dev remains NULL.
The PCIe bandwidth controller erroneously does not check for a NULL
subordinate pointer and dereferences it on probe.
Bandwidth control of unusable devices below the bridge is of questionable
utility, so simply error out instead. This mirrors what PCIe hotplug does
since commit 62e4492c3063 ("PCI: Prevent NULL dereference during pciehp
probe").
The PCI core emits a message with KERN_INFO severity if it has run out of
bus numbers. PCIe hotplug emits an additional message with KERN_ERR
severity to inform the user that hotplug functionality is disabled at the
bridge. A similar message for bandwidth control does not seem merited,
given that its only purpose so far is to expose an up-to-date link speed
in sysfs and throttle the link speed on certain laptops with limited
Thermal Design Power. So error out silently.
User-visible messages:
pci 0000:16:02.0: bridge configuration invalid ([bus 00-00]), reconfiguring
[...]
pci_bus 0000:45: busn_res: [bus 45-74] end is updated to 74
pci 0000:16:02.0: devices behind bridge are unusable because [bus 45-74] cannot be assigned for them
[...]
pcieport 0000:16:02.0: pciehp: Hotplug bridge without secondary bus, ignoring
[...]
BUG: kernel NULL pointer dereference
RIP: pcie_update_link_speed
pcie_bwnotif_enable
pcie_bwnotif_probe
pcie_port_probe_service
really_probe
Fixes: 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller")
Reported-by: Wouter Bijlsma <wouter@wouterbijlsma.nl>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219906
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Tested-by: Wouter Bijlsma <wouter@wouterbijlsma.nl>
Cc: stable@vger.kernel.org # v6.13+
Link: https://lore.kernel.org/r/3b6c8d973aedc48860640a9d75d20528336f1f3c.1742669372.git.lukas@wunner.de
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pcie_bwctrl_select_speed() should take __fls() of the speed bit, not return
it as a raw value. Instead of directly returning 2.5GT/s speed bit, simply
assign the fallback speed (2.5GT/s) into supported_speeds variable to share
the normal return path that calls pcie_supported_speeds2target_speed() to
calculate __fls().
This code path is not very likely to execute because
pcie_get_supported_speeds() should provide valid ->supported_speeds but a
spec violating device could fail to synthesize any speed in
pcie_get_supported_speeds(). It could also happen in case the
supported_speeds intersection is empty (also a violation of the current
PCIe specs).
Link: https://lore.kernel.org/r/20250321163103.5145-1-ilpo.jarvinen@linux.intel.com
Fixes: de9a6c8d5dbf ("PCI/bwctrl: Add pcie_set_target_speed() to set PCIe Link Speed")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
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The interrupt handler for bandwidth notifications, pcie_bwnotif_irq(),
dereferences a "data" pointer.
On unbind, that pointer is set to NULL by pcie_bwnotif_remove(). However
the interrupt handler may still be invoked afterwards and will dereference
that NULL pointer.
That's because the interrupt is requested using a devm_*() helper and the
driver core releases devm_*() resources *after* calling ->remove().
pcie_bwnotif_remove() does clear the Link Bandwidth Management Interrupt
Enable and Link Autonomous Bandwidth Interrupt Enable bits in the Link
Control Register, but that won't prevent execution of pcie_bwnotif_irq():
The interrupt for bandwidth notifications may be shared with AER, DPC,
PME, and hotplug. So pcie_bwnotif_irq() may be executed as long as the
interrupt is requested.
There's a similar race on bind: pcie_bwnotif_probe() requests the
interrupt when the "data" pointer still points to NULL. A NULL pointer
deref may thus likewise occur if AER, DPC, PME or hotplug raise an
interrupt in-between the bandwidth controller's call to devm_request_irq()
and assignment of the "data" pointer.
Drop the devm_*() usage and reorder requesting of the interrupt to fix the
issue.
While at it, drop a stray but harmless no_free_ptr() invocation when
assigning the "data" pointer in pcie_bwnotif_probe().
Ilpo points out that the locking on unbind and bind needs to be symmetric,
so move the call to pcie_bwnotif_disable() inside the critical section
protected by pcie_bwctrl_setspeed_rwsem and pcie_bwctrl_lbms_rwsem.
Evert reports a hang on shutdown of an ASUS ROG Strix SCAR 17 G733PYV.
The issue is no longer reproducible with the present commit.
Evert found that attaching a USB-C monitor prevented the hang. The
machine contains an ASMedia USB 3.2 controller below a hotplug-capable
Root Port. So one possible explanation is that the controller gets
hot-removed on shutdown unless something is connected. And the ensuing
hotplug interrupt occurs exactly when the bandwidth controller is
unregistering. The precise cause could not be determined because the
screen had already turned black when the hang occurred.
Link: https://lore.kernel.org/r/ae2b02c9cfbefff475b6e132b0aa962aaccbd7b2.1736162539.git.lukas@wunner.de
Fixes: 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller")
Reported-by: Evert Vorster <evorster@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219629
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Evert Vorster <evorster@gmail.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
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Add a thermal cooling driver to provide path to access PCIe bandwidth
controller using the usual thermal interfaces.
A cooling device is instantiated for controllable PCIe Ports from the
bwctrl service driver.
If registering the cooling device fails, allow bwctrl's probe to succeed
regardless. As cdev in that case contains IS_ERR() pseudo "pointer", clean
that up inside the probe function so the remove side doesn't need to
suddenly make an odd looking IS_ERR() check.
The thermal side state 0 means no throttling, i.e., maximum supported PCIe
Link Speed.
Link: https://lore.kernel.org/r/20241018144755.7875-9-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
[bhelgaas: dropped data->cdev test per
https://lore.kernel.org/r/ZzRm1SJTwEMRsAr8@wunner.de]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org> # From the cooling device interface perspective
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Currently, PCIe Link Speeds are adjusted by custom code rather than in a
common function provided in PCI core. The PCIe bandwidth controller
(bwctrl) introduces an in-kernel API, pcie_set_target_speed(), 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, which requires the per port
mutex (set_speed_mutex) to be only taken if the bwctrl setup is already
complete.
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.
Link: https://lore.kernel.org/r/20241018144755.7875-8-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
[bhelgaas: squash devm_mutex_init() error checking from
https://lore.kernel.org/r/20241030163139.2111689-1-andriy.shevchenko@linux.intel.com,
drop export of pcie_set_target_speed()]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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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
<mr.nuke.me@gmail.com>; see e8303bb7a75c ("PCI/LINK: Report degraded links
via link bandwidth notification")]
Link: https://lore.kernel.org/r/20241018144755.7875-7-ilpo.jarvinen@linux.intel.com
Link: https://lore.kernel.org/all/20190429185611.121751-1-helgaas@kernel.org/
Link: https://lore.kernel.org/linux-pci/20190501142942.26972-1-keith.busch@intel.com/
Link: https://lore.kernel.org/linux-pci/20200115221008.GA191037@google.com/
Suggested-by: Lukas Wunner <lukas@wunner.de> # Building bwctrl on top of bwnotif
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
[bhelgaas: squash fix to drop IRQF_ONESHOT and convert to hardirq handler:
https://lore.kernel.org/r/20241115165717.15233-1-ilpo.jarvinen@linux.intel.com]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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