irqchip: mips-cpu: Introduce IPI IRQ domain support

Introduce support for registering an IPI IRQ domain suitable for use by
systems using the MIPS MT (multithreading) ASE within a single core.
This will allow for such systems to be supported generically, without
the current kludge of IPI code split between the MIPS arch & the malta
board support code.

Signed-off-by: Paul Burton <[e-mail]>
Acked-by: Thomas Gleixner <[e-mail]>
Cc: Jason Cooper <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/15836/
Signed-off-by: Ralf Baechle <[e-mail]>

drivers/irqchip/Kconfig

···
 config IRQ_MIPS_CPU
 	bool
 	select GENERIC_IRQ_CHIP
+	select GENERIC_IRQ_IPI if SYS_SUPPORTS_MULTITHREADING
 	select IRQ_DOMAIN
+	select IRQ_DOMAIN_HIERARCHY if GENERIC_IRQ_IPI
 
 config CLPS711X_IRQCHIP
 	bool

drivers/irqchip/irq-mips-cpu.c

···
 /*
  * Almost all MIPS CPUs define 8 interrupt sources.  They are typically
  * level triggered (i.e., cannot be cleared from CPU; must be cleared from
- * device).  The first two are software interrupts which we don't really
- * use or support.  The last one is usually the CPU timer interrupt if
- * counter register is present or, for CPUs with an external FPU, by
- * convention it's the FPU exception interrupt.
+ * device).
  *
- * Don't even think about using this on SMP.  You have been warned.
+ * The first two are software interrupts (i.e. not exposed as pins) which
+ * may be used for IPIs in multi-threaded single-core systems.
  *
- * This file exports one global function:
- *	void mips_cpu_irq_init(void);
+ * The last one is usually the CPU timer interrupt if the counter register
+ * is present, or for old CPUs with an external FPU by convention it's the
+ * FPU exception interrupt.
  */
 #include <linux/init.h>
 #include <linux/interrupt.h>
···
 #include <asm/setup.h>
 
 static struct irq_domain *irq_domain;
+static struct irq_domain *ipi_domain;
 
 static inline void unmask_mips_irq(struct irq_data *d)
 {
···
 	mask_mips_irq(d);
 }
 
+#ifdef CONFIG_GENERIC_IRQ_IPI
+
+static void mips_mt_send_ipi(struct irq_data *d, unsigned int cpu)
+{
+	irq_hw_number_t hwirq = irqd_to_hwirq(d);
+	unsigned long flags;
+	int vpflags;
+
+	local_irq_save(flags);
+
+	/* We can only send IPIs to VPEs within the local core */
+	WARN_ON(cpu_data[cpu].core != current_cpu_data.core);
+
+	vpflags = dvpe();
+	settc(cpu_vpe_id(&cpu_data[cpu]));
+	write_vpe_c0_cause(read_vpe_c0_cause() | (C_SW0 << hwirq));
+	evpe(vpflags);
+
+	local_irq_restore(flags);
+}
+
+#endif /* CONFIG_GENERIC_IRQ_IPI */
+
 static struct irq_chip mips_mt_cpu_irq_controller = {
 	.name		= "MIPS",
 	.irq_startup	= mips_mt_cpu_irq_startup,
···
 	.irq_eoi	= unmask_mips_irq,
 	.irq_disable	= mask_mips_irq,
 	.irq_enable	= unmask_mips_irq,
+#ifdef CONFIG_GENERIC_IRQ_IPI
+	.ipi_send_single = mips_mt_send_ipi,
+#endif
 };
 
 asmlinkage void __weak plat_irq_dispatch(void)
···
 	pending >>= CAUSEB_IP;
 	while (pending) {
 		irq = fls(pending) - 1;
-		virq = irq_linear_revmap(irq_domain, irq);
+		if (IS_ENABLED(CONFIG_GENERIC_IRQ_IPI) && irq < 2)
+			virq = irq_linear_revmap(ipi_domain, irq);
+		else
+			virq = irq_linear_revmap(irq_domain, irq);
 		do_IRQ(virq);
 		pending &= ~BIT(irq);
 	}
···
 	.xlate = irq_domain_xlate_onecell,
 };
 
+#ifdef CONFIG_GENERIC_IRQ_IPI
+
+struct cpu_ipi_domain_state {
+	DECLARE_BITMAP(allocated, 2);
+};
+
+static int mips_cpu_ipi_alloc(struct irq_domain *domain, unsigned int virq,
+			      unsigned int nr_irqs, void *arg)
+{
+	struct cpu_ipi_domain_state *state = domain->host_data;
+	unsigned int i, hwirq;
+	int ret;
+
+	for (i = 0; i < nr_irqs; i++) {
+		hwirq = find_first_zero_bit(state->allocated, 2);
+		if (hwirq == 2)
+			return -EBUSY;
+		bitmap_set(state->allocated, hwirq, 1);
+
+		ret = irq_domain_set_hwirq_and_chip(domain, virq + i, hwirq,
+						    &mips_mt_cpu_irq_controller,
+						    NULL);
+		if (ret)
+			return ret;
+
+		ret = irq_set_irq_type(virq + i, IRQ_TYPE_LEVEL_HIGH);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int mips_cpu_ipi_match(struct irq_domain *d, struct device_node *node,
+			      enum irq_domain_bus_token bus_token)
+{
+	bool is_ipi;
+
+	switch (bus_token) {
+	case DOMAIN_BUS_IPI:
+		is_ipi = d->bus_token == bus_token;
+		return (!node || (to_of_node(d->fwnode) == node)) && is_ipi;
+	default:
+		return 0;
+	}
+}
+
+static const struct irq_domain_ops mips_cpu_ipi_chip_ops = {
+	.alloc	= mips_cpu_ipi_alloc,
+	.match	= mips_cpu_ipi_match,
+};
+
+static void mips_cpu_register_ipi_domain(struct device_node *of_node)
+{
+	struct cpu_ipi_domain_state *ipi_domain_state;
+
+	ipi_domain_state = kzalloc(sizeof(*ipi_domain_state), GFP_KERNEL);
+	ipi_domain = irq_domain_add_hierarchy(irq_domain,
+					      IRQ_DOMAIN_FLAG_IPI_SINGLE,
+					      2, of_node,
+					      &mips_cpu_ipi_chip_ops,
+					      ipi_domain_state);
+	if (!ipi_domain)
+		panic("Failed to add MIPS CPU IPI domain");
+	ipi_domain->bus_token = DOMAIN_BUS_IPI;
+}
+
+#else /* !CONFIG_GENERIC_IRQ_IPI */
+
+static inline void mips_cpu_register_ipi_domain(struct device_node *of_node) {}
+
+#endif /* !CONFIG_GENERIC_IRQ_IPI */
+
 static void __init __mips_cpu_irq_init(struct device_node *of_node)
 {
 	/* Mask interrupts. */
···
 					   NULL);
 	if (!irq_domain)
 		panic("Failed to add irqdomain for MIPS CPU");
+
+	/*
+	 * Only proceed to register the software interrupt IPI implementation
+	 * for CPUs which implement the MIPS MT (multi-threading) ASE.
+	 */
+	if (cpu_has_mipsmt)
+		mips_cpu_register_ipi_domain(of_node);
 }
 
 void __init mips_cpu_irq_init(void)