[PATCH v3 4/7] riscv: Clear pending IPIs on initialization

[Sean Anderson]

Even though we no longer call smp_function if an IPI was not sent by
U-Boot, we still need to clear any IPIs which were pending from the
execution environment. Otherwise, secondary harts will busy-wait in
secondary_hart_loop, instead of relaxing.

Along with the previous commit ("riscv: Use a valid bit to ignore
already-pending IPIs"), this fixes SMP booting on the Kendryte K210.

Signed-off-by: Sean Anderson <seanga2 at gmail.com>
Reviewed-by: Bin Meng <bin.meng at windriver.com>

---

Changes in v3:
- Rename riscv_ipi_init_secondary_hart to dummy_pending_ipi_clear
- Only compile dummy_pending_ipi_clear when SMP is enabled

Changes in v2:
- Make riscv_ipi_init_secondary_hart static

 arch/riscv/cpu/cpu.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
index bfa2d4a426..85592f5bee 100644
--- a/arch/riscv/cpu/cpu.c
+++ b/arch/riscv/cpu/cpu.c
@@ -72,6 +72,17 @@ static int riscv_cpu_probe(void)
 	return 0;
 }
 
+/*
+ * This is called on secondary harts just after the IPI is init'd. Currently
+ * there's nothing to do, since we just need to clear any existing IPIs, and
+ * that is handled by the sending of an ipi itself.
+ */
+#if CONFIG_IS_ENABLED(SMP)
+static void dummy_pending_ipi_clear(ulong hart, ulong arg0, ulong arg1)
+{
+}
+#endif
+
 int arch_cpu_init_dm(void)
 {
 	int ret;
@@ -111,6 +122,15 @@ int arch_cpu_init_dm(void)
 	ret = riscv_init_ipi();
 	if (ret)
 		return ret;
+
+	/*
+	 * Clear all pending IPIs on secondary harts. We don't do anything on
+	 * the boot hart, since we never send an IPI to ourselves, and no
+	 * interrupts are enabled
+	 */
+	ret = smp_call_function((ulong)dummy_pending_ipi_clear, 0, 0, 0);
+	if (ret)
+		return ret;
 #endif
 
 	return 0;
-- 
2.28.0