RISC-V: Treat IPIs as normal Linux IRQs

Currently, the RISC-V kernel provides arch specific hooks (i.e.
struct riscv_ipi_ops) to register IPI handling methods. The stats
gathering of IPIs is also arch specific in the RISC-V kernel.

Other architectures (such as ARM, ARM64, and MIPS) have moved away
from custom arch specific IPI handling methods. Currently, these
architectures have Linux irqchip drivers providing a range of Linux
IRQ numbers to be used as IPIs and IPI triggering is done using
generic IPI APIs. This approach allows architectures to treat IPIs
as normal Linux IRQs and IPI stats gathering is done by the generic
Linux IRQ subsystem.

We extend the RISC-V IPI handling as-per above approach so that arch
specific IPI handling methods (struct riscv_ipi_ops) can be removed
and the IPI handling is done through the Linux IRQ subsystem.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230328035223.1480939-4-apatel@ventanamicro.com

1 files changed, 49 insertions, 16 deletions

diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index 6cfe2ab73eb0..7ccc16dd6a76 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -17,6 +17,9 @@
 #include <linux/sched_clock.h>
 #include <linux/io-64-nonatomic-lo-hi.h>
 #include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/irqchip/chained_irq.h>
+#include <linux/irqdomain.h>
 #include <linux/of_irq.h>
 #include <linux/smp.h>
 #include <linux/timex.h>
@@ -31,6 +34,7 @@
 
 /* CLINT manages IPI and Timer for RISC-V M-mode  */
 static u32 __iomem *clint_ipi_base;
+static unsigned int clint_ipi_irq;
 static u64 __iomem *clint_timer_cmp;
 static u64 __iomem *clint_timer_val;
 static unsigned long clint_timer_freq;
@@ -41,12 +45,10 @@ u64 __iomem *clint_time_val;
 EXPORT_SYMBOL(clint_time_val);
 #endif
 
-static void clint_send_ipi(const struct cpumask *target)
+#ifdef CONFIG_SMP
+static void clint_send_ipi(unsigned int cpu)
 {
-	unsigned int cpu;
-
-	for_each_cpu(cpu, target)
-		writel(1, clint_ipi_base + cpuid_to_hartid_map(cpu));
+	writel(1, clint_ipi_base + cpuid_to_hartid_map(cpu));
 }
 
 static void clint_clear_ipi(void)
@@ -54,10 +56,18 @@ static void clint_clear_ipi(void)
 	writel(0, clint_ipi_base + cpuid_to_hartid_map(smp_processor_id()));
 }
 
-static struct riscv_ipi_ops clint_ipi_ops = {
-	.ipi_inject = clint_send_ipi,
-	.ipi_clear = clint_clear_ipi,
-};
+static void clint_ipi_interrupt(struct irq_desc *desc)
+{
+	struct irq_chip *chip = irq_desc_get_chip(desc);
+
+	chained_irq_enter(chip, desc);
+
+	clint_clear_ipi();
+	ipi_mux_process();
+
+	chained_irq_exit(chip, desc);
+}
+#endif
 
 #ifdef CONFIG_64BIT
 #define clint_get_cycles()	readq_relaxed(clint_timer_val)
@@ -125,12 +135,19 @@ static int clint_timer_starting_cpu(unsigned int cpu)
 
 	enable_percpu_irq(clint_timer_irq,
 			  irq_get_trigger_type(clint_timer_irq));
+	enable_percpu_irq(clint_ipi_irq,
+			  irq_get_trigger_type(clint_ipi_irq));
 	return 0;
 }
 
 static int clint_timer_dying_cpu(unsigned int cpu)
 {
 	disable_percpu_irq(clint_timer_irq);
+	/*
+	 * Don't disable IPI when CPU goes offline because
+	 * the masking/unmasking of virtual IPIs is done
+	 * via generic IPI-Mux
+	 */
 	return 0;
 }
 
@@ -170,6 +187,12 @@ static int __init clint_timer_init_dt(struct device_node *np)
 			return -ENODEV;
 		}
 
+		/* Find parent irq domain and map ipi irq */
+		if (!clint_ipi_irq &&
+		    oirq.args[0] == RV_IRQ_SOFT &&
+		    irq_find_host(oirq.np))
+			clint_ipi_irq = irq_of_parse_and_map(np, i);
+
 		/* Find parent irq domain and map timer irq */
 		if (!clint_timer_irq &&
 		    oirq.args[0] == RV_IRQ_TIMER &&
@@ -177,9 +200,9 @@ static int __init clint_timer_init_dt(struct device_node *np)
 			clint_timer_irq = irq_of_parse_and_map(np, i);
 	}
 
-	/* If CLINT timer irq not found then fail */
-	if (!clint_timer_irq) {
-		pr_err("%pOFP: timer irq not found\n", np);
+	/* If CLINT ipi or timer irq not found then fail */
+	if (!clint_ipi_irq || !clint_timer_irq) {
+		pr_err("%pOFP: ipi/timer irq not found\n", np);
 		return -ENODEV;
 	}
 
@@ -219,6 +242,19 @@ static int __init clint_timer_init_dt(struct device_node *np)
 		goto fail_iounmap;
 	}
 
+#ifdef CONFIG_SMP
+	rc = ipi_mux_create(BITS_PER_BYTE, clint_send_ipi);
+	if (rc <= 0) {
+		pr_err("unable to create muxed IPIs\n");
+		rc = (rc < 0) ? rc : -ENODEV;
+		goto fail_free_irq;
+	}
+
+	irq_set_chained_handler(clint_ipi_irq, clint_ipi_interrupt);
+	riscv_ipi_set_virq_range(rc, BITS_PER_BYTE);
+	clint_clear_ipi();
+#endif
+
 	rc = cpuhp_setup_state(CPUHP_AP_CLINT_TIMER_STARTING,
 				"clockevents/clint/timer:starting",
 				clint_timer_starting_cpu,
@@ -228,13 +264,10 @@ static int __init clint_timer_init_dt(struct device_node *np)
 		goto fail_free_irq;
 	}
 
-	riscv_set_ipi_ops(&clint_ipi_ops);
-	clint_clear_ipi();
-
 	return 0;
 
 fail_free_irq:
-	free_irq(clint_timer_irq, &clint_clock_event);
+	free_percpu_irq(clint_timer_irq, &clint_clock_event);
 fail_iounmap:
 	iounmap(base);
 	return rc;