irqchip/mips-gic: Add new DT property to reserve IPIs

The new property will allow to specify the range of GIC hwirqs to use for IPIs.

This is an optinal property. We preserve the previous behaviour of allocating
the last 2 * gic_vpes if it's not specified or DT is not supported.

Signed-off-by: Qais Yousef <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Acked-by: Ralf Baechle <[e-mail]>
Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: Qais Yousef <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

Documentation/devicetree/bindings/interrupt-controller/mips-gic.txt

···
 - mti,reserved-cpu-vectors : Specifies the list of CPU interrupt vectors
   to which the GIC may not route interrupts.  Valid values are 2 - 7.
   This property is ignored if the CPU is started in EIC mode.
+- mti,reserved-ipi-vectors : Specifies the range of GIC interrupts that are
+  reserved for IPIs.
+  It accepts 2 values, the 1st is the starting interrupt and the 2nd is the size
+  of the reserved range.
+  If not specified, the driver will allocate the last 2 * number of VPEs in the
+  system.
 
 Required properties for timer sub-node:
 - compatible : Should be "mti,gic-timer".
···
 		#interrupt-cells = <3>;
 
 		mti,reserved-cpu-vectors = <7>;
+		mti,reserved-ipi-vectors = <40 8>;
 
 		timer {
 			compatible = "mti,gic-timer";

drivers/irqchip/irq-mips-gic.c

···
 			      struct device_node *node)
 {
 	unsigned int gicconfig;
+	unsigned int v[2];
 
 	__gic_base_addr = gic_base_addr;
 
···
 
 	gic_ipi_domain->bus_token = DOMAIN_BUS_IPI;
 
-	/* Make the last 2 * gic_vpes available for IPIs */
-	bitmap_set(ipi_resrv, gic_shared_intrs - 2 * gic_vpes, 2 * gic_vpes);
+	if (node &&
+	    !of_property_read_u32_array(node, "mti,reserved-ipi-vectors", v, 2)) {
+		bitmap_set(ipi_resrv, v[0], v[1]);
+	} else {
+		/* Make the last 2 * gic_vpes available for IPIs */
+		bitmap_set(ipi_resrv,
+			   gic_shared_intrs - 2 * gic_vpes,
+			   2 * gic_vpes);
+	}
 
 	gic_basic_init();
 }