irqchip/sifive-plic: Setup cpuhp once after boot CPU handler is present

For multiple PLIC instances, the plic_init() is called once for each
PLIC instance. Due to this we have two issues:
1. cpuhp_setup_state() is called multiple times
2. plic_starting_cpu() can crash for boot CPU if cpuhp_setup_state()
   is called before boot CPU PLIC handler is available.

Address both issues by only initializing the HP notifiers when
the boot CPU setup is complete.

Fixes: f1ad1133 ("irqchip/sifive-plic: Add support for multiple PLICs")
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200518091441.94843-3-anup.patel@wdc.com

drivers/irqchip/irq-sifive-plic.c

@@ -76,6 +76,7 @@ struct plic_handler {
 	void __iomem		*enable_base;
 	struct plic_priv	*priv;
 };
+static bool plic_cpuhp_setup_done;
 static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
 
 static inline void plic_toggle(struct plic_handler *handler,
@@ -285,6 +286,7 @@ static int __init plic_init(struct device_node *node,
 	int error = 0, nr_contexts, nr_handlers = 0, i;
 	u32 nr_irqs;
 	struct plic_priv *priv;
+	struct plic_handler *handler;
 
 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -313,7 +315,6 @@ static int __init plic_init(struct device_node *node,
 
 	for (i = 0; i < nr_contexts; i++) {
 		struct of_phandle_args parent;
-		struct plic_handler *handler;
 		irq_hw_number_t hwirq;
 		int cpu, hartid;
 
@@ -367,9 +368,18 @@ static int __init plic_init(struct device_node *node,
 		nr_handlers++;
 	}
 
-	cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
+	/*
+	 * We can have multiple PLIC instances so setup cpuhp state only
+	 * when context handler for current/boot CPU is present.
+	 */
+	handler = this_cpu_ptr(&plic_handlers);
+	if (handler->present && !plic_cpuhp_setup_done) {
+		cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
 				  "irqchip/sifive/plic:starting",
 				  plic_starting_cpu, plic_dying_cpu);
+		plic_cpuhp_setup_done = true;
+	}
+
 	pr_info("mapped %d interrupts with %d handlers for %d contexts.\n",
 		nr_irqs, nr_handlers, nr_contexts);
 	set_handle_irq(plic_handle_irq);