Re: [PATCH 2/3] pci/hotplug/pnv_php: Work around switches with broken presence detection

[Lukas Wunner]

[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@xxxxxxxxxxxxxxxx/

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