[PATCH v10 12/12] irqchip/sifive-plic: Initialize the plic handler when cpu comes online

[Atish Patra <atish.patra@wdc.com>]

Currently, plic threshold and priority are only initialized once in the
beginning. However, threshold can be set to disabled if cpu is marked
offline with cpu hotplug feature. This will not allow to change the
irq affinity to a cpu that just came online.

Add plic specific cpu hotplug callback and initialize the per cpu handler
when cpu comes online.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
---
 arch/riscv/kernel/traps.c         |  2 +-
 drivers/irqchip/irq-sifive-plic.c | 38 +++++++++++++++++++++++++++----
 include/linux/cpuhotplug.h        |  1 +
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 8e13ad45ccaa..16c59807da6a 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -157,5 +157,5 @@ void trap_init(void)
 	/* Set the exception vector address */
 	csr_write(CSR_TVEC, &handle_exception);
 	/* Enable interrupts */
-	csr_write(CSR_IE, IE_SIE | IE_EIE);
+	csr_write(CSR_IE, IE_SIE);
 }
diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index aa4af886e43a..7c7f37393f99 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2018 Christoph Hellwig
  */
 #define pr_fmt(fmt) "plic: " fmt
+#include <linux/cpu.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/irq.h>
@@ -55,6 +56,9 @@
 #define     CONTEXT_THRESHOLD		0x00
 #define     CONTEXT_CLAIM		0x04
 
+#define	PLIC_DISABLE_THRESHOLD		0xf
+#define	PLIC_ENABLE_THRESHOLD		0
+
 static void __iomem *plic_regs;
 
 struct plic_handler {
@@ -230,6 +234,32 @@ static int plic_find_hart_id(struct device_node *node)
 	return -1;
 }
 
+static void plic_set_threshold(struct plic_handler *handler, u32 threshold)
+{
+	/* priority must be > threshold to trigger an interrupt */
+	writel(threshold, handler->hart_base + CONTEXT_THRESHOLD);
+}
+
+static int plic_dying_cpu(unsigned int cpu)
+{
+	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
+
+	csr_clear(CSR_IE, IE_EIE);
+	plic_set_threshold(handler, PLIC_DISABLE_THRESHOLD);
+
+	return 0;
+}
+
+static int plic_starting_cpu(unsigned int cpu)
+{
+	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
+
+	csr_set(CSR_IE, IE_EIE);
+	plic_set_threshold(handler, PLIC_ENABLE_THRESHOLD);
+
+	return 0;
+}
+
 static int __init plic_init(struct device_node *node,
 		struct device_node *parent)
 {
@@ -267,7 +297,6 @@ 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);
@@ -301,7 +330,7 @@ static int __init plic_init(struct device_node *node,
 		handler = per_cpu_ptr(&plic_handlers, cpu);
 		if (handler->present) {
 			pr_warn("handler already present for context %d.\n", i);
-			threshold = 0xffffffff;
+			plic_set_threshold(handler, PLIC_DISABLE_THRESHOLD);
 			goto done;
 		}
 
@@ -313,13 +342,14 @@ static int __init plic_init(struct device_node *node,
 			plic_regs + ENABLE_BASE + i * ENABLE_PER_HART;
 
 done:
-		/* priority must be > threshold to trigger an interrupt */
-		writel(threshold, handler->hart_base + CONTEXT_THRESHOLD);
 		for (hwirq = 1; hwirq <= nr_irqs; hwirq++)
 			plic_toggle(handler, hwirq, 0);
 		nr_handlers++;
 	}
 
+	cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
+				  "irqchip/sifive/plic:starting",
+				  plic_starting_cpu, plic_dying_cpu);
 	pr_info("mapped %d interrupts with %d handlers for %d contexts.\n",
 		nr_irqs, nr_handlers, nr_contexts);
 	set_handle_irq(plic_handle_irq);
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index d37c17e68268..77d70b633531 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -102,6 +102,7 @@ enum cpuhp_state {
 	CPUHP_AP_IRQ_ARMADA_XP_STARTING,
 	CPUHP_AP_IRQ_BCM2836_STARTING,
 	CPUHP_AP_IRQ_MIPS_GIC_STARTING,
+	CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
 	CPUHP_AP_ARM_MVEBU_COHERENCY,
 	CPUHP_AP_MICROCODE_LOADER,
 	CPUHP_AP_PERF_X86_AMD_UNCORE_STARTING,
-- 
2.25.0