Re: [PATCH v2 2/6] pci/hotplug/pnv_php: Work around switches with broken
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2025-06-18 19:44:01
Also in:
linux-pci, lkml
[+cc Lukas, pciehp expert] On Wed, Jun 18, 2025 at 11:56:54AM -0500, Timothy Pearson wrote:
presence detection
(subject/commit wrapping seems to be on all of these patches)
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.
Seems like this switch supports standard PCIe hotplug? Quite a bit of this driver looks similar to things in pciehp. Is there some reason we can't use pciehp directly? Maybe pciehp could work if there were hooks for the PPC-specific bits?
quoted hunk ↗ jump to hunk
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 <redacted> 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