Re: [PATCH v2 2/6] pci/hotplug/pnv_php: Work around switches with broken

[Bjorn Helgaas <helgaas@kernel.org>]

[+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?

> 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