Re: [PATCH v3 05/10] drm/xe/xe_ras: Initialize Uncorrectable AER Registers

[Raag Jadav <raag.jadav@intel.com>]

On Thu, Apr 02, 2026 at 12:31:36PM +0530, Riana Tauro wrote:
> Uncorrectable errors from different endpoints in the device are steered to
> the USP which is a PCI Advanced Error Reporting (AER) Compliant device.

See below.

> Downgrade all the errors to non-fatal to prevent PCIe bus driver
> from triggering a Secondary Bus Reset (SBR). This allows error
> detection, containment and recovery in the driver.
> 
> The Uncorrectable Error Severity Register has the 'Uncorrectable
> Internal Error Severity' set to fatal by default. Set this to
> non-fatal and unmask the error.

...

> +static void aer_unmask_and_downgrade_internal_error(struct xe_device *xe)
> +{
> +	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> +	struct pci_dev *vsp, *usp;
> +	u32 aer_uncorr_mask, aer_uncorr_sev, aer_uncorr_status;
> +	u16 aer_cap;
> +
> +	 /* Gfx Device Hierarchy: USP-->VSP-->SGunit */

What are these TLAs and why is everyone expected to know them?

> +	vsp = pci_upstream_bridge(pdev);
> +	if (!vsp)
> +		return;
> +
> +	usp = pci_upstream_bridge(vsp);
> +	if (!usp)
> +		return;
> +
> +	aer_cap = usp->aer_cap;
> +
> +	if (!aer_cap)
> +		return;
> +
> +	/*
> +	 * Clear any stale Uncorrectable Internal Error Status event in Uncorrectable Error
> +	 * Status Register.
> +	 */
> +	pci_read_config_dword(usp, aer_cap + PCI_ERR_UNCOR_STATUS, &aer_uncorr_status);
> +	if (aer_uncorr_status & PCI_ERR_UNC_INTN)
> +		pci_write_config_dword(usp, aer_cap + PCI_ERR_UNCOR_STATUS, PCI_ERR_UNC_INTN);
> +
> +	/*
> +	 * All errors are steered to USP which is a PCIe AER Compliant device.

Ditto.

Raag

> +	 * Downgrade all the errors to non-fatal to prevent PCIe bus driver
> +	 * from triggering a Secondary Bus Reset (SBR). This allows error
> +	 * detection, containment and recovery in the driver.
> +	 *
> +	 * The Uncorrectable Error Severity Register has the 'Uncorrectable
> +	 * Internal Error Severity' set to fatal by default. Set this to
> +	 * non-fatal and unmask the error.
> +	 */