ARM: 7177/1: GIC: avoid skipping non-existent PPIs in irq_start calculation

Commit 4294f8ba ("ARM: gic: add irq_domain support") defines irq_start
as irq_start = (irq_start & ~31) + 16; On a platform with a GIC and a
CPU without PPIs, this results in irq_start being off by 16.

This patch fixes gic_init so that we only carve out a PPI space when
PPIs exist for the GIC being initialised.

Cc: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/common/gic.c

@@ -582,13 +582,16 @@ void __init gic_init(unsigned int gic_nr, int irq_start,
 	 * For primary GICs, skip over SGIs.
 	 * For secondary GICs, skip over PPIs, too.
 	 */
+	domain->hwirq_base = 32;
 	if (gic_nr == 0) {
 		gic_cpu_base_addr = cpu_base;
-		domain->hwirq_base = 16;
-		if (irq_start > 0)
-			irq_start = (irq_start & ~31) + 16;
-	} else
-		domain->hwirq_base = 32;
+
+		if ((irq_start & 31) > 0) {
+			domain->hwirq_base = 16;
+			if (irq_start != -1)
+				irq_start = (irq_start & ~31) + 16;
+		}
+	}
 
 	/*
 	 * Find out how many interrupts are supported.