[PATCH v3 2/6] PCI: pnv_php: Work around switches with broken presence detection

Timothy Pearson
2025-07-15T21:36:56Z

The Microsemi Switchtec PM8533 PFX 48xG3 [11f8:8533] PCIe switch system
was observed to incorrectly assert the Presence Detect Set bit in its
capabilities when tested on a Raptor Computing Systems Blackbird system,
resulting in the hot insert path never attempting a rescan of the bus
and any downstream devices not being re-detected.

Work around this by additionally checking whether the PCIe data link is
active or not when performing presence detection on downstream switches'
ports, similar to the pciehp_hpc.c driver.

Signed-off-by: Shawn Anastasio <sanastasio@raptorengineering.com>
Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
---
drivers/pci/hotplug/pnv_php.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/drivers/pci/hotplug/pnv_php.c b/drivers/pci/hotplug/pnv_php.c
index aec0a6d594ac..bac8af3df41a 100644
--- a/drivers/pci/hotplug/pnv_php.c
+++ b/drivers/pci/hotplug/pnv_php.c
@@ -391,6 +391,20 @@ static int pnv_php_get_power_state(struct hotplug_slot *slot, u8 *state)
return 0;
}

+static int pcie_check_link_active(struct pci_dev *pdev)
+{
+ u16 lnk_status;
+ int ret;
+
+ ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
+ if (ret == PCIBIOS_DEVICE_NOT_FOUND || PCI_POSSIBLE_ERROR(lnk_status))
+ return -ENODEV;
+
+ ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
+
+ return ret;
+}
+
static int pnv_php_get_adapter_state(struct hotplug_slot *slot, u8 *state)
{
struct pnv_php_slot *php_slot = to_pnv_php_slot(slot);
@@ -403,6 +417,19 @@ static int pnv_php_get_adapter_state(struct hotplug_slot *slot, u8 *state)
*/
ret = pnv_pci_get_presence_state(php_slot->id, &presence);
if (ret >= 0) {
+ if (pci_pcie_type(php_slot->pdev) == PCI_EXP_TYPE_DOWNSTREAM &&
+ presence == OPAL_PCI_SLOT_EMPTY) {
+ /*
+ * Similar to pciehp_hpc, check whether the Link Active
+ * bit is set to account for broken downstream bridges
+ * that don't properly assert Presence Detect State, as
+ * was observed on the Microsemi Switchtec PM8533 PFX
+ * [11f8:8533].
+ */
+ if (pcie_check_link_active(php_slot->pdev) > 0)
+ presence = OPAL_PCI_SLOT_PRESENT;
+ }
+
*state = presence;
ret = 0;
} else {
--
2.39.5