irqchip/gic-v3: Warn about inconsistent implementations of extended ranges

As is it usual for the GIC, it isn't disallowed to put together a system
that is majorly inconsistent, with a distributor supporting the
extended ranges while some of the CPUs don't.

Kindly tell the user that things are sailing isn't going to be smooth.
Signed-off-by: Marc Zyngier <maz@kernel.org>

drivers/irqchip/irq-gic-v3.c

@@ -1014,6 +1014,11 @@ static void gic_cpu_init(void)
 
 	gic_enable_redist(true);
 
+	WARN((gic_data.ppi_nr > 16 || GIC_ESPI_NR != 0) &&
+	     !(gic_read_ctlr() & ICC_CTLR_EL1_ExtRange),
+	     "Distributor has extended ranges, but CPU%d doesn't\n",
+	     smp_processor_id());
+
 	rbase = gic_data_rdist_sgi_base();
 
 	/* Configure SGIs/PPIs as non-secure Group-1 */

include/linux/irqchip/arm-gic-v3.h

@@ -496,6 +496,7 @@
 #define ICC_CTLR_EL1_A3V_SHIFT		15
 #define ICC_CTLR_EL1_A3V_MASK		(0x1 << ICC_CTLR_EL1_A3V_SHIFT)
 #define ICC_CTLR_EL1_RSS		(0x1 << 18)
+#define ICC_CTLR_EL1_ExtRange		(0x1 << 19)
 #define ICC_PMR_EL1_SHIFT		0
 #define ICC_PMR_EL1_MASK		(0xff << ICC_PMR_EL1_SHIFT)
 #define ICC_BPR0_EL1_SHIFT		0