[RFC PATCH v3 08/17] ACPI: RISC-V: Implement arch function to reorder irqchip probe entries

[Sunil V L]

ACPI MADT entries for interrupt controllers don't have a way to describe
the hierarchy. However, the hierarchy is known to the architecture and
on RISC-V platforms, the MADT sub table types are ordered in the
incremental order from the root controller which is RINTC. So, add
architecture function for RISC-V to reorder the interrupt controller
probing as per the hierarchy as below.

RINTC->IMSIC->APLIC->PLIC

Signed-off-by: Sunil V L <sunilvl at ventanamicro.com>
---
 drivers/acpi/riscv/Makefile |  2 +-
 drivers/acpi/riscv/irq.c    | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 drivers/acpi/riscv/irq.c

diff --git a/drivers/acpi/riscv/Makefile b/drivers/acpi/riscv/Makefile
index 8b3b126e0b94..f80b3da230e9 100644
--- a/drivers/acpi/riscv/Makefile
+++ b/drivers/acpi/riscv/Makefile
@@ -1,2 +1,2 @@
 # SPDX-License-Identifier: GPL-2.0-only
-obj-y 	+= rhct.o
+obj-y 	+= rhct.o irq.o
diff --git a/drivers/acpi/riscv/irq.c b/drivers/acpi/riscv/irq.c
new file mode 100644
index 000000000000..36e0525b3235
--- /dev/null
+++ b/drivers/acpi/riscv/irq.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023, Ventana Micro Systems Inc
+ *	Author: Sunil V L <sunilvl at ventanamicro.com>
+ *
+ */
+
+#include <linux/acpi.h>
+#include <linux/sort.h>
+
+static int irqchip_cmp_func(const void *in0, const void *in1)
+{
+	struct acpi_probe_entry *elem0 = (struct acpi_probe_entry *)in0;
+	struct acpi_probe_entry *elem1 = (struct acpi_probe_entry *)in1;
+
+	return (elem0->type > elem1->type) - (elem0->type < elem1->type);
+}
+
+/*
+ * RISC-V irqchips in MADT of ACPI spec are defined in the same order how
+ * they should be probed. Since IRQCHIP_ACPI_DECLARE doesn't define any
+ * order, this arch function will reorder the probe functions as per the
+ * required order for the architecture.
+ */
+void arch_sort_irqchip_probe(struct acpi_probe_entry *ap_head, int nr)
+{
+	struct acpi_probe_entry *ape = ap_head;
+
+	if (nr == 1 || !ACPI_COMPARE_NAMESEG(ACPI_SIG_MADT, ape->id))
+		return;
+	sort(ape, nr, sizeof(*ape), irqchip_cmp_func, NULL);
+}
-- 
2.39.2