irqchip: mips-gic: SYNC after enabling GIC region

A SYNC is required between enabling the GIC region and actually trying
to use it, even if the first access is a read, otherwise its possible
depending on the timing (and in my case depending on the precise
alignment of certain kernel code) to hit CM bus errors on that first
access.

Add the SYNC straight after setting the GIC base.

[[email protected]:
  Changes later in this series increase our likelihood of hitting this
  by reducing the amount of code that runs between enabling the GIC &
  accessing it.]

Fixes: a705727 ("irqchip: mips-gic: Add device-tree support")
Signed-off-by: James Hogan <[email protected]>
Signed-off-by: Paul Burton <[email protected]>
Acked-by: Marc Zyngier <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Jason Cooper <[email protected]>
Cc: James Hogan <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: <[email protected]> # 3.19.x-
Patchwork: https://patchwork.linux-mips.org/patch/17019/
Signed-off-by: Ralf Baechle <[email protected]>

Author: James Hogan

drivers/irqchip/irq-mips-gic.c

@@ -1020,8 +1020,11 @@ static int __init gic_of_init(struct device_node *node,
 		gic_len = resource_size(&res);
 	}
 
-	if (mips_cm_present())
+	if (mips_cm_present()) {
 		write_gcr_gic_base(gic_base | CM_GCR_GIC_BASE_GICEN_MSK);
+		/* Ensure GIC region is enabled before trying to access it */
+		__sync();
+	}
 	gic_present = true;
 
 	__gic_init(gic_base, gic_len, cpu_vec, 0, node);