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: 5352a44a561d ("PCI: pciehp: Make pciehp_is_native() stricter")
Reported-by: Laurent Bigonville <bigon@xxxxxxxx>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220216
Reported-by: Mario Limonciello <mario.limonciello@xxxxxxx>
Closes: https://lore.kernel.org/r/20250609020223.269407-3-superm1@xxxxxxxxxx/
Link: https://lore.kernel.org/all/20250620025535.3425049-3-superm1@xxxxxxxxxx/T/#u
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.18+
---
drivers/pci/pci-acpi.c | 4 +---
drivers/pci/pci.c | 6 +++++-
drivers/pci/probe.c | 2 +-
include/linux/pci.h | 6 ++++++
4 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index b78e0e417324..efe478e5073e 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -816,13 +816,11 @@ int pci_acpi_program_hp_params(struct pci_dev *dev)
bool pciehp_is_native(struct pci_dev *bridge)
{
const struct pci_host_bridge *host;
- u32 slot_cap;
if (!IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
return false;
- pcie_capability_read_dword(bridge, PCI_EXP_SLTCAP, &slot_cap);
- if (!(slot_cap & PCI_EXP_SLTCAP_HPC))
+ if (!bridge->is_pciehp)
return false;
if (pcie_ports_native)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e9448d55113b..23d8fe98ddf9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3030,8 +3030,12 @@ static const struct dmi_system_id bridge_d3_blacklist[] = {
* pci_bridge_d3_possible - Is it possible to put the bridge into D3
* @bridge: Bridge to check
*
- * This function checks if it is possible to move the bridge to D3.
* Currently we only allow D3 for some PCIe ports and for Thunderbolt.
+ *
+ * Return: Whether it is possible to move the bridge to D3.
+ *
+ * The return value is guaranteed to be constant across the entire lifetime
+ * of the bridge, including its hot-removal.
*/
bool pci_bridge_d3_possible(struct pci_dev *bridge)
{
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4b8693ec9e4c..cf50be63bf5f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1678,7 +1678,7 @@ void set_pcie_hotplug_bridge(struct pci_dev *pdev)
pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, ®32);
if (reg32 & PCI_EXP_SLTCAP_HPC)
- pdev->is_hotplug_bridge = 1;
+ pdev->is_hotplug_bridge = pdev->is_pciehp = 1;
}
static void set_pcie_thunderbolt(struct pci_dev *dev)
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 05e68f35f392..d56d0dd80afb 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -328,6 +328,11 @@ struct rcec_ea;
* determined (e.g., for Root Complex Integrated
* Endpoints without the relevant Capability
* Registers).
+ * @is_hotplug_bridge: Hotplug bridge of any kind (e.g. PCIe Hot-Plug Capable,
+ * Conventional PCI Hot-Plug, ACPI slot).
+ * Such bridges are allocated additional MMIO and bus
+ * number resources to allow for hierarchy expansion.
+ * @is_pciehp: PCIe Hot-Plug Capable bridge.
*/
struct pci_dev {
struct list_head bus_list; /* Node in per-bus list */
@@ -451,6 +456,7 @@ struct pci_dev {
unsigned int is_physfn:1;
unsigned int is_virtfn:1;
unsigned int is_hotplug_bridge:1;
+ unsigned int is_pciehp:1;
unsigned int shpc_managed:1; /* SHPC owned by shpchp */
unsigned int is_thunderbolt:1; /* Thunderbolt controller */
/*
--
2.47.2
