[RFC PATCH v1 03/10] RISC-V: Allow more details in IPI operations

[Anup Patel]

We extend struct riscv_ipi_ops so that the IPI providers (such as
SBI, CLINT driver, ACLINT SWI driver etc) can specify:
1) Name of the IPI operations
2) Whether IPIs are suitable for doing remote FENCEs

Signed-off-by: Anup Patel <anup.patel at wdc.com>
---
 arch/riscv/include/asm/smp.h      | 15 +++++++++++++++
 arch/riscv/kernel/sbi.c           |  2 ++
 arch/riscv/kernel/smp.c           | 25 ++++++++++++++++++++++++-
 arch/riscv/mm/cacheflush.c        |  2 +-
 drivers/clocksource/timer-clint.c |  2 ++
 5 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
index a7d2811f3536..4c4f0dde1164 100644
--- a/arch/riscv/include/asm/smp.h
+++ b/arch/riscv/include/asm/smp.h
@@ -16,11 +16,16 @@ struct seq_file;
 extern unsigned long boot_cpu_hartid;
 
 struct riscv_ipi_ops {
+	const char *name;
+	bool use_for_rfence;
 	void (*ipi_inject)(const struct cpumask *target);
 	void (*ipi_clear)(void);
 };
 
 #ifdef CONFIG_SMP
+
+#include <linux/jump_label.h>
+
 /*
  * Mapping between linux logical cpu index and hartid.
  */
@@ -45,6 +50,11 @@ void arch_send_call_function_single_ipi(int cpu);
 int riscv_hartid_to_cpuid(int hartid);
 void riscv_cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask *out);
 
+/* Check if we can use IPIs for remote FENCE */
+extern struct static_key_false riscv_ipi_for_rfence;
+#define riscv_use_ipi_for_rfence() \
+	static_branch_unlikely(&riscv_ipi_for_rfence)
+
 /* Set custom IPI operations */
 void riscv_set_ipi_ops(const struct riscv_ipi_ops *ops);
 
@@ -92,6 +102,11 @@ static inline void riscv_cpuid_to_hartid_mask(const struct cpumask *in,
 	cpumask_set_cpu(boot_cpu_hartid, out);
 }
 
+static inline bool riscv_use_ipi_for_rfence(void)
+{
+	return false;
+}
+
 static inline void riscv_set_ipi_ops(const struct riscv_ipi_ops *ops)
 {
 }
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 8aeca26198f2..be2b7a89ce49 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -604,6 +604,8 @@ static void sbi_ipi_clear(void)
 }
 
 static const struct riscv_ipi_ops sbi_ipi_ops = {
+	.name = "SBI",
+	.use_for_rfence = false,
 	.ipi_inject = sbi_send_cpumask_ipi,
 	.ipi_clear = sbi_ipi_clear
 };
diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
index eea0c9d11d9f..cffe3247b132 100644
--- a/arch/riscv/kernel/smp.c
+++ b/arch/riscv/kernel/smp.c
@@ -90,9 +90,32 @@ static void ipi_stop(void)
 
 static const struct riscv_ipi_ops *ipi_ops __ro_after_init;
 
+DEFINE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
+EXPORT_SYMBOL_GPL(riscv_ipi_for_rfence);
+
 void riscv_set_ipi_ops(const struct riscv_ipi_ops *ops)
 {
-	ipi_ops = ops;
+	bool updated = true;
+
+	if (!ops)
+		return;
+
+	if (!ipi_ops) {
+		ipi_ops = ops;
+	} else {
+		if (!ipi_ops->use_for_rfence && ops->use_for_rfence)
+			ipi_ops = ops;
+		else
+			updated = false;
+	}
+
+	if (updated) {
+		if (ipi_ops->use_for_rfence)
+			static_branch_enable(&riscv_ipi_for_rfence);
+		else
+			static_branch_disable(&riscv_ipi_for_rfence);
+		pr_info("switched IPI operations to %s\n", ipi_ops->name);
+	}
 }
 EXPORT_SYMBOL_GPL(riscv_set_ipi_ops);
 
diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
index 094118663285..0ffe7d560dc8 100644
--- a/arch/riscv/mm/cacheflush.c
+++ b/arch/riscv/mm/cacheflush.c
@@ -16,7 +16,7 @@ static void ipi_remote_fence_i(void *info)
 
 void flush_icache_all(void)
 {
-	if (IS_ENABLED(CONFIG_RISCV_SBI))
+	if (!riscv_use_ipi_for_rfence())
 		sbi_remote_fence_i(NULL);
 	else
 		on_each_cpu(ipi_remote_fence_i, NULL, 1);
diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index 6cfe2ab73eb0..dfdcd94c1fd5 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -55,6 +55,8 @@ static void clint_clear_ipi(void)
 }
 
 static struct riscv_ipi_ops clint_ipi_ops = {
+	.name = "CLINT",
+	.use_for_rfence = true,
 	.ipi_inject = clint_send_ipi,
 	.ipi_clear = clint_clear_ipi,
 };
-- 
2.25.1