IRQCHIP: mips-gic: Add function for retrieving FDC IRQ

Add a function to the MIPS GIC driver for retrieving the Fast Debug
Channel (FDC) interrupt number, similar to the existing ones for the
timer and perf counter interrupts. This will be used by platform
implementations of get_c0_fdc_int() if a GIC is present.

A workaround exists for interAptiv and proAptiv which claim to be able
to route the FDC interrupt but don't seem to be able to in practice (at
least on Malta).

[ralf@linux-mips.org: Fix conflict.]
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9142/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

drivers/irqchip/irq-mips-gic.c

@@ -227,6 +227,29 @@ int gic_get_c0_perfcount_int(void)
 				  GIC_LOCAL_TO_HWIRQ(GIC_LOCAL_INT_PERFCTR));
 }
 
+int gic_get_c0_fdc_int(void)
+{
+	if (!gic_local_irq_is_routable(GIC_LOCAL_INT_FDC)) {
+		/* Is the FDC IRQ even present? */
+		if (cp0_fdc_irq < 0)
+			return -1;
+		return MIPS_CPU_IRQ_BASE + cp0_fdc_irq;
+	}
+
+	/*
+	 * Some cores claim the FDC is routable but it doesn't actually seem to
+	 * be connected.
+	 */
+	switch (current_cpu_type()) {
+	case CPU_INTERAPTIV:
+	case CPU_PROAPTIV:
+		return -1;
+	}
+
+	return irq_create_mapping(gic_irq_domain,
+				  GIC_LOCAL_TO_HWIRQ(GIC_LOCAL_INT_FDC));
+}
+
 static void gic_handle_shared_int(void)
 {
 	unsigned int i, intr, virq;

include/linux/irqchip/mips-gic.h

@@ -251,4 +251,5 @@ extern unsigned int plat_ipi_call_int_xlate(unsigned int);
 extern unsigned int plat_ipi_resched_int_xlate(unsigned int);
 extern int gic_get_c0_compare_int(void);
 extern int gic_get_c0_perfcount_int(void);
+extern int gic_get_c0_fdc_int(void);
 #endif /* __LINUX_IRQCHIP_MIPS_GIC_H */