powerpc/pci: Fix regression in powerpc MSI-X

Patch f598282f exposed a problem in
powerpc MSI-X functionality, making network interfaces such as ixgbe
and cxgb3 stop to work when MSI-X is enabled. RX interrupts were not
being generated.

The problem was caused because MSI irq was not being effectively
unmasked after device initialization.
Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/msi.c

@@ -432,8 +432,6 @@ static int rtas_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
 		/* Read config space back so we can restore after reset */
 		read_msi_msg(virq, &msg);
 		entry->msg = msg;
-
-		unmask_msi_irq(virq);
 	}
 
 	return 0;

arch/powerpc/platforms/pseries/xics.c

@@ -18,6 +18,7 @@
 #include <linux/init.h>
 #include <linux/radix-tree.h>
 #include <linux/cpu.h>
+#include <linux/msi.h>
 #include <linux/of.h>
 
 #include <asm/firmware.h>
@@ -219,6 +220,14 @@ static void xics_unmask_irq(unsigned int virq)
 
 static unsigned int xics_startup(unsigned int virq)
 {
+	/*
+	 * The generic MSI code returns with the interrupt disabled on the
+	 * card, using the MSI mask bits. Firmware doesn't appear to unmask
+	 * at that level, so we do it here by hand.
+	 */
+	if (irq_to_desc(virq)->msi_desc)
+		unmask_msi_irq(virq);
+
 	/* unmask it */
 	xics_unmask_irq(virq);
 	return 0;