[PATCH v8 5/7] RISC-V: Allow marking IPIs as suitable for remote FENCEs

[Anup Patel]

To do remote FENCEs (i.e. remote TLB flushes) using IPI calls on the
RISC-V kernel, we need hardware mechanism to directly inject IPI from
the supervisor mode (i.e. RISC-V kernel) instead of using SBI calls.

The upcoming AIA IMSIC devices allow direct IPI injection from the
supervisor mode (i.e. RISC-V kernel). To support this, we extend the
riscv_ipi_set_virq_range() function so that IPI provider (i.e. irqchip
drivers can mark IPIs as suitable for remote FENCEs.

Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
---
 arch/riscv/include/asm/smp.h      | 18 ++++++++++++++++--
 arch/riscv/kernel/sbi-ipi.c       |  2 +-
 arch/riscv/kernel/smp.c           | 11 ++++++++++-
 drivers/clocksource/timer-clint.c |  2 +-
 4 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
index 79ed0b73cd4e..56976e41a21e 100644
--- a/arch/riscv/include/asm/smp.h
+++ b/arch/riscv/include/asm/smp.h
@@ -16,6 +16,9 @@ struct seq_file;
 extern unsigned long boot_cpu_hartid;
 
 #ifdef CONFIG_SMP
+
+#include <linux/jump_label.h>
+
 /*
  * Mapping between linux logical cpu index and hartid.
  */
@@ -46,7 +49,12 @@ void riscv_ipi_disable(void);
 bool riscv_ipi_have_virq_range(void);
 
 /* Set the IPI interrupt numbers for arch (called by irqchip drivers) */
-void riscv_ipi_set_virq_range(int virq, int nr);
+void riscv_ipi_set_virq_range(int virq, int nr, bool use_for_rfence);
+
+/* Check if we can use IPIs for remote FENCEs */
+DECLARE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
+#define riscv_use_ipi_for_rfence() \
+	static_branch_unlikely(&riscv_ipi_for_rfence)
 
 /* Secondary hart entry */
 asmlinkage void smp_callin(void);
@@ -93,10 +101,16 @@ static inline bool riscv_ipi_have_virq_range(void)
 	return false;
 }
 
-static inline void riscv_ipi_set_virq_range(int virq, int nr)
+static inline void riscv_ipi_set_virq_range(int virq, int nr,
+					    bool use_for_rfence)
 {
 }
 
+static inline bool riscv_use_ipi_for_rfence(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_SMP */
 
 #if defined(CONFIG_HOTPLUG_CPU) && (CONFIG_SMP)
diff --git a/arch/riscv/kernel/sbi-ipi.c b/arch/riscv/kernel/sbi-ipi.c
index 0bb070a5dcb4..27fdc394d2f0 100644
--- a/arch/riscv/kernel/sbi-ipi.c
+++ b/arch/riscv/kernel/sbi-ipi.c
@@ -55,6 +55,6 @@ void __init sbi_ipi_init(void)
 		return;
 	}
 
-	riscv_ipi_set_virq_range(virq, BITS_PER_BYTE);
+	riscv_ipi_set_virq_range(virq, BITS_PER_BYTE, false);
 	pr_info("providing IPIs using SBI IPI extension\n");
 }
diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
index e25d39cd2d27..cb2bda4822de 100644
--- a/arch/riscv/kernel/smp.c
+++ b/arch/riscv/kernel/smp.c
@@ -143,7 +143,10 @@ bool riscv_ipi_have_virq_range(void)
 	return (ipi_virq_base) ? true : false;
 }
 
-void riscv_ipi_set_virq_range(int virq, int nr)
+DEFINE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
+EXPORT_SYMBOL_GPL(riscv_ipi_for_rfence);
+
+void riscv_ipi_set_virq_range(int virq, int nr, bool use_for_rfence)
 {
 	int i, err;
 
@@ -166,6 +169,12 @@ void riscv_ipi_set_virq_range(int virq, int nr)
 
 	/* Enabled IPIs for boot CPU immediately */
 	riscv_ipi_enable();
+
+	/* Update RFENCE static key */
+	if (use_for_rfence)
+		static_branch_enable(&riscv_ipi_for_rfence);
+	else
+		static_branch_disable(&riscv_ipi_for_rfence);
 }
 EXPORT_SYMBOL_GPL(riscv_ipi_set_virq_range);
 
diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index ac7c2caaa65a..f418816fd706 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -246,7 +246,7 @@ static int __init clint_timer_init_dt(struct device_node *np)
 		goto fail_remove_cpuhp;
 	}
 
-	riscv_ipi_set_virq_range(virq, BITS_PER_BYTE);
+	riscv_ipi_set_virq_range(virq, BITS_PER_BYTE, true);
 	clint_clear_ipi(clint_ipi_irq, NULL);
 
 	return 0;
-- 
2.34.1