cxl: Do not create vPHB if there are no AFU configuration records

The vPHB model of the cxl kernel API is a hierarchy where the AFU is
represented by the vPHB, and it's AFU configuration records are exposed
as functions under that vPHB. If there are no AFU configuration records
we will create a vPHB with nothing under it, which is a waste of
resources and will opt us into EEH handling despite not having anything
special to handle.

This also does not make sense for cards using the peer model of the cxl
kernel API, where the other functions of the device are exposed via
additional peer physical functions rather than AFU configuration
records. This model will also not work with the existing EEH handling in
the cxl driver, as that is designed around the vPHB model.

Skip creating the vPHB for AFUs without any AFU configuration records,
and opt out of EEH handling for them.
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/pci.c

@@ -1572,6 +1572,9 @@ static pci_ers_result_t cxl_pci_error_detected(struct pci_dev *pdev,
 		 */
 		for (i = 0; i < adapter->slices; i++) {
 			afu = adapter->afu[i];
+			/* Only participate in EEH if we are on a virtual PHB */
+			if (afu->phb == NULL)
+				return PCI_ERS_RESULT_NONE;
 			cxl_vphb_error_detected(afu, state);
 		}
 		return PCI_ERS_RESULT_DISCONNECT;

drivers/misc/cxl/vphb.c

@@ -188,6 +188,17 @@ int cxl_pci_vphb_add(struct cxl_afu *afu)
 	struct device_node *vphb_dn;
 	struct device *parent;
 
+	/*
+	 * If there are no AFU configuration records we won't have anything to
+	 * expose under the vPHB, so skip creating one, returning success since
+	 * this is still a valid case. This will also opt us out of EEH
+	 * handling since we won't have anything special to do if there are no
+	 * kernel drivers attached to the vPHB, and EEH handling is not yet
+	 * supported in the peer model.
+	 */
+	if (!afu->crs_num)
+		return 0;
+
 	/* The parent device is the adapter. Reuse the device node of
 	 * the adapter.
 	 * We don't seem to care what device node is used for the vPHB,