irqchip/sifive-plic: set max threshold for ignored handlers

When running in M-mode, the S-mode plic handlers are still listed in the
device tree.  Ignore them by setting the maximum threshold.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

drivers/irqchip/irq-sifive-plic.c

@@ -244,6 +244,7 @@ static int __init plic_init(struct device_node *node,
 		struct plic_handler *handler;
 		irq_hw_number_t hwirq;
 		int cpu, hartid;
+		u32 threshold = 0;
 
 		if (of_irq_parse_one(node, i, &parent)) {
 			pr_err("failed to parse parent for context %d.\n", i);
@@ -266,10 +267,16 @@ static int __init plic_init(struct device_node *node,
 			continue;
 		}
 
+		/*
+		 * When running in M-mode we need to ignore the S-mode handler.
+		 * Here we assume it always comes later, but that might be a
+		 * little fragile.
+		 */
 		handler = per_cpu_ptr(&plic_handlers, cpu);
 		if (handler->present) {
 			pr_warn("handler already present for context %d.\n", i);
-			continue;
+			threshold = 0xffffffff;
+			goto done;
 		}
 
 		handler->present = true;
@@ -279,8 +286,9 @@ static int __init plic_init(struct device_node *node,
 		handler->enable_base =
 			plic_regs + ENABLE_BASE + i * ENABLE_PER_HART;
 
+done:
 		/* priority must be > threshold to trigger an interrupt */
-		writel(0, handler->hart_base + CONTEXT_THRESHOLD);
+		writel(threshold, handler->hart_base + CONTEXT_THRESHOLD);
 		for (hwirq = 1; hwirq <= nr_irqs; hwirq++)
 			plic_toggle(handler, hwirq, 0);
 		nr_handlers++;