riscv: add functions for reading the IPI status

Add the function riscv_get_ipi() for reading the pending status of IPIs.
The supported controllers are Andes' Platform Level Interrupt Controller
(PLIC), the Supervisor Binary Interface (SBI), and SiFive's Core Local
Interruptor (CLINT).

Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Rick Chen <rick@andestech.com>

arch/riscv/lib/andes_plic.c

@@ -117,6 +117,17 @@ int riscv_clear_ipi(int hart)
 	return 0;
 }
 
+int riscv_get_ipi(int hart, int *pending)
+{
+	PLIC_BASE_GET();
+
+	*pending = readl((void __iomem *)PENDING_REG(gd->arch.plic,
+						     gd->arch.boot_hart));
+	*pending = !!(*pending & SEND_IPI_TO_HART(hart));
+
+	return 0;
+}
+
 static const struct udevice_id andes_plic_ids[] = {
 	{ .compatible = "riscv,plic1", .data = RISCV_SYSCON_PLIC },
 	{ }

arch/riscv/lib/sbi_ipi.c

@@ -23,3 +23,14 @@ int riscv_clear_ipi(int hart)
 
 	return 0;
 }
+
+int riscv_get_ipi(int hart, int *pending)
+{
+	/*
+	 * The SBI does not support reading the IPI status. We always return 0
+	 * to indicate that no IPI is pending.
+	 */
+	*pending = 0;
+
+	return 0;
+}

arch/riscv/lib/sifive_clint.c

@@ -71,6 +71,15 @@ int riscv_clear_ipi(int hart)
 	return 0;
 }
 
+int riscv_get_ipi(int hart, int *pending)
+{
+	CLINT_BASE_GET();
+
+	*pending = readl((void __iomem *)MSIP_REG(gd->arch.clint, hart));
+
+	return 0;
+}
+
 static const struct udevice_id sifive_clint_ids[] = {
 	{ .compatible = "riscv,clint0", .data = RISCV_SYSCON_CLINT },
 	{ }

arch/riscv/lib/smp.c

@@ -32,6 +32,18 @@ extern int riscv_send_ipi(int hart);
  */
 extern int riscv_clear_ipi(int hart);
 
+/**
+ * riscv_get_ipi() - Get status of inter-processor interrupt (IPI)
+ *
+ * Platform code must provide this function.
+ *
+ * @hart: Hart ID of hart to be checked
+ * @pending: Pointer to variable with result of the check,
+ *           1 if IPI is pending, 0 otherwise
+ * @return 0 if OK, -ve on error
+ */
+extern int riscv_get_ipi(int hart, int *pending);
+
 static int send_ipi_many(struct ipi_data *ipi)
 {
 	ofnode node, cpus;