powerpc/powernv: Call opal_pci_poll() if needed

BugLink: https://bugs.launchpad.net/bugs/1652018

When issuing PHB reset, OPAL API opal_pci_poll() is called to drive
the state machine in OPAL forward. However, we needn't always call
the function under some circumstances like reset deassert.

This avoids calling opal_pci_poll() when OPAL_SUCCESS is returned
from opal_pci_reset(). Except the overhead introduced by additional
one unnecessary OPAL call, I didn't run into real issue because of
this.
Reported-by: Pridhiviraj Paidipeddi <ppaiddipe@in.ibm.com>
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(backported from commit fbce44d0)
[cascardo: use original pnv_eeh_phb_poll]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

arch/powerpc/platforms/powernv/eeh-powernv.c

@@ -777,7 +777,8 @@ int pnv_eeh_phb_reset(struct pci_controller *hose, int option)
 	 * reset followed by hot reset on root bus. So we also
 	 * need the PCI bus settlement delay.
 	 */
-	rc = pnv_eeh_phb_poll(phb);
+	if (rc > 0)
+		rc = pnv_eeh_phb_poll(phb);
 	if (option == EEH_RESET_DEACTIVATE) {
 		if (system_state < SYSTEM_RUNNING)
 			udelay(1000 * EEH_PE_RST_SETTLE_TIME);
@@ -820,7 +821,8 @@ static int pnv_eeh_root_reset(struct pci_controller *hose, int option)
 		goto out;
 
 	/* Poll state of the PHB until the request is done */
-	rc = pnv_eeh_phb_poll(phb);
+	if (rc > 0)
+		rc = pnv_eeh_phb_poll(phb);
 	if (option == EEH_RESET_DEACTIVATE)
 		msleep(EEH_PE_RST_SETTLE_TIME);
 out: