Re: [PATCH v8 5/6] drm/xe: Suppress Surprise Link Down on device

[Lukas Wunner <lukas@wunner.de>]

On Fri, Jun 12, 2026 at 01:37:28PM +0530, Mallesh Koujalagi wrote:
> PUNIT errors can only be recovered using a power-cycle. Xe KMD
> sends a uevent to notify userspace to trigger a power cycle.
> On platforms where link drop caused by powering the device off and
> back on is reported by hardware as a Surprise Link Down (SLD), which
> AER then escalates as an Uncorrectable Fatal Error. That error fires
> before the device finishes coming back up and defeats the
> very recovery we are attempting.
> 
> To keep the expected, recovery-induced link drop from being raised as
> a fatal AER event, mask the Surprise Link Down bit
> (PCI_ERR_UNC_SURPDN) in the upstream port's AER Uncorrectable Error
> Mask register before punit_error_handler() requests the cold reset.

You need to clear the Surprise Down Error Status bit in the
Uncorrectable Error Status Register after the reset.

You should also unmask the error.

> +	pci_read_config_dword(usp, aer_cap + PCI_ERR_UNCOR_MASK, &aer_uncorr_mask);
> +	aer_uncorr_mask |= PCI_ERR_UNC_SURPDN;
> +	pci_write_config_dword(usp, aer_cap + PCI_ERR_UNCOR_MASK, aer_uncorr_mask);

pci_clear_and_set_config_dword()?

OSPM is not supposed to fiddle with AER registers unless it has been
granted control of those registers through the ACPI _OSC method.

There's a pcie_aer_is_native() helper to skip access to those registers
but its only visible to the PCI core currently.

Thanks,

Lukas