powerpc/eeh: Enable IO path on permanent error

We give up recovery on permanent error, simply shutdown the affected
devices and remove them. If the devices can't be put into quiet state,
they spew more traffic that is likely to cause another unexpected EEH
error. This was observed on "p8dtu2u" machine:

   0002:00:00.0 PCI bridge: IBM Device 03dc
   0002:01:00.0 Ethernet controller: Intel Corporation \
                Ethernet Controller X710/X557-AT 10GBASE-T (rev 02)
   0002:01:00.1 Ethernet controller: Intel Corporation \
                Ethernet Controller X710/X557-AT 10GBASE-T (rev 02)
   0002:01:00.2 Ethernet controller: Intel Corporation \
                Ethernet Controller X710/X557-AT 10GBASE-T (rev 02)
   0002:01:00.3 Ethernet controller: Intel Corporation \
                Ethernet Controller X710/X557-AT 10GBASE-T (rev 02)

On P8 PowerNV platform, the IO path is frozen when shutdowning the
devices, meaning the memory registers are inaccessible. It is why
the devices can't be put into quiet state before removing them.
This fixes the issue by enabling IO path prior to putting the devices
into quiet state.
Reported-by: NPridhiviraj Paidipeddi <ppaidipe@linux.vnet.ibm.com>
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Acked-by: NRussell Currey <ruscur@russell.cc>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/eeh.c

@@ -298,9 +298,17 @@ void eeh_slot_error_detail(struct eeh_pe *pe, int severity)
 	 *
 	 * For pHyp, we have to enable IO for log retrieval. Otherwise,
 	 * 0xFF's is always returned from PCI config space.
+	 *
+	 * When the @severity is EEH_LOG_PERM, the PE is going to be
+	 * removed. Prior to that, the drivers for devices included in
+	 * the PE will be closed. The drivers rely on working IO path
+	 * to bring the devices to quiet state. Otherwise, PCI traffic
+	 * from those devices after they are removed is like to cause
+	 * another unexpected EEH error.
 	 */
 	if (!(pe->type & EEH_PE_PHB)) {
-		if (eeh_has_flag(EEH_ENABLE_IO_FOR_LOG))
+		if (eeh_has_flag(EEH_ENABLE_IO_FOR_LOG) ||
+		    severity == EEH_LOG_PERM)
 			eeh_pci_enable(pe, EEH_OPT_THAW_MMIO);
 
 		/*