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>
---
 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 2c07544216fb..1a734adb5b10 100644
--- a/drivers/pci/hotplug/pnv_php.c
+++ b/drivers/pci/hotplug/pnv_php.c
@@ -390,6 +390,20 @@ 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);
@@ -402,6 +416,19 @@ 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 {
-- 
2.30.2

[cc += Krishna]

On Thu, Apr 03, 2025 at 11:18:09PM -0500, Shawn Anastasio wrote:
> 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.
[...]
> --- a/drivers/pci/hotplug/pnv_php.c
> +++ b/drivers/pci/hotplug/pnv_php.c
> @@ -390,6 +390,20 @@ 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;
> +}
> +

This appears to be a 1:1 copy of pciehp_check_link_active(),
save for the ctrl_dbg() call.

For the sake of code-reuse, please move the function into the
PCI library drivers/pci/pci.c so that it can be used everywhere.

Note that there's another patch pending which does exactly that:

https://lore.kernel.org/r/20250225-qps615_v4_1-v4-7-e08633a7bdf8@oss.qualcomm.com/

So either include that patch in your series (addressing the review
feedback I sent for it and cc'ing the original submitter) or wait
for it to be respun by the original submitter.

Thanks,

Lukas

On Fri, Apr 04, 2025 at 06:42:32AM +0200, Lukas Wunner wrote:
> On Thu, Apr 03, 2025 at 11:18:09PM -0500, Shawn Anastasio wrote:
> > 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.
> [...]
> > --- a/drivers/pci/hotplug/pnv_php.c
> > +++ b/drivers/pci/hotplug/pnv_php.c
> > @@ -390,6 +390,20 @@ 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;
> > +}
> > +
> 
> This appears to be a 1:1 copy of pciehp_check_link_active(),
> save for the ctrl_dbg() call.
> 
> For the sake of code-reuse, please move the function into the
> PCI library drivers/pci/pci.c so that it can be used everywhere.
> 
> Note that there's another patch pending which does exactly that:
> 
> https://lore.kernel.org/r/20250225-qps615_v4_1-v4-7-e08633a7bdf8@oss.qualcomm.com/
> 
> So either include that patch in your series (addressing the review
> feedback I sent for it and cc'ing the original submitter) or wait
> for it to be respun by the original submitter.

Update -- Krishna respun the patch:

https://lore.kernel.org/r/20250412-qps615_v4_1-v5-7-5b6a06132fec@oss.qualcomm.com/