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[ Upstream commit 6cff20ce3b92ffbf2fc5eb9e5a030b3672aa414a ]
pci_bridge_d3_possible() is called from both pcie_portdrv_probe() and
pcie_portdrv_remove() to determine whether runtime power management shall
be enabled (on probe) or disabled (on remove) on a PCIe port.
The underlying assumption is that pci_bridge_d3_possible() always returns
the same value, else a runtime PM reference imbalance would occur. That
assumption is not given if the PCIe port is inaccessible on remove due to
hot-unplug: pci_bridge_d3_possible() calls pciehp_is_native(), which
accesses Config Space to determine whether the port is Hot-Plug Capable.
An inaccessible port returns "all ones", which is converted to "all
zeroes" by pcie_capability_read_dword(). Hence the port no longer seems
Hot-Plug Capable on remove even though it was on probe.
The resulting runtime PM ref imbalance causes warning messages such as:
pcieport 0000:02:04.0: Runtime PM usage count underflow!
Avoid the Config Space access (and thus the runtime PM ref imbalance) by
caching the Hot-Plug Capable bit in struct pci_dev.
The struct already contains an "is_hotplug_bridge" flag, which however is
not only set on Hot-Plug Capable PCIe ports, but also Conventional PCI
Hot-Plug bridges and ACPI slots. The flag identifies bridges which are
allocated additional MMIO and bus number resources to allow for hierarchy
expansion.
The kernel is somewhat sloppily using "is_hotplug_bridge" in a number of
places to identify Hot-Plug Capable PCIe ports, even though the flag
encompasses other devices. Subsequent commits replace these occurrences
with the new flag to clearly delineate Hot-Plug Capable PCIe ports from
other kinds of hotplug bridges.
Document the existing "is_hotplug_bridge" and the new "is_pciehp" flag
and document the (non-obvious) requirement that pci_bridge_d3_possible()
always returns the same value across the entire lifetime of a bridge,
including its hot-removal.
Fixes: 5352a44a56 ("PCI: pciehp: Make pciehp_is_native() stricter")
Reported-by: Laurent Bigonville <bigon@bigon.be>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220216
Reported-by: Mario Limonciello <mario.limonciello@amd.com>
Closes: https://lore.kernel.org/r/20250609020223.269407-3-superm1@kernel.org/
Link: https://lore.kernel.org/all/20250620025535.3425049-3-superm1@kernel.org/T/#u
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Cc: stable@vger.kernel.org # v4.18+
Link: https://patch.msgid.link/fe5dcc3b2e62ee1df7905d746bde161eb1b3291c.1752390101.git.lukas@wunner.de
[ changed "recent enough PCIe ports" comment to "some PCIe ports" ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.