[PATCH v8 10/17] ACPI: RISC-V: Implement function to reorder irqchip probe entries

[Sunil V L <sunilvl@ventanamicro.com>]

On RISC-V platforms, the RINTC structures should be probed before any
other interrupt controller structures and IMSIC before APLIC. This order
is established by using MADT sub table types which are ordered in the
incremental order from the RINTC. So, add the architecture function for
RISC-V to reorder the interrupt controller probing as per the hierarchy
like below.

  ACPI_MADT_TYPE_RINTC = 24,
  ACPI_MADT_TYPE_IMSIC = 25,
  ACPI_MADT_TYPE_APLIC = 26,
  ACPI_MADT_TYPE_PLIC = 27

This means processing all RINTC structures (in the order of appearance
in MADT), followed by IMSIC strucutre and then all APLIC/PLIC
structures.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
---
 drivers/acpi/riscv/Makefile |  2 +-
 drivers/acpi/riscv/irq.c    | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 drivers/acpi/riscv/irq.c

diff --git a/drivers/acpi/riscv/Makefile b/drivers/acpi/riscv/Makefile
index 877de00d1b50..a96fdf1e2cb8 100644
--- a/drivers/acpi/riscv/Makefile
+++ b/drivers/acpi/riscv/Makefile
@@ -1,4 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
-obj-y					+= rhct.o init.o
+obj-y					+= rhct.o init.o irq.o
 obj-$(CONFIG_ACPI_PROCESSOR_IDLE)	+= cpuidle.o
 obj-$(CONFIG_ACPI_CPPC_LIB)		+= cppc.o
diff --git a/drivers/acpi/riscv/irq.c b/drivers/acpi/riscv/irq.c
new file mode 100644
index 000000000000..835eb6eccd53
--- /dev/null
+++ b/drivers/acpi/riscv/irq.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023-2024, Ventana Micro Systems Inc
+ *	Author: Sunil V L <sunilvl@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);
+}
+
+/*
+ * On RISC-V, RINTC structures in MADT should be probed before any other
+ * interrupt controller structures and IMSIC before APLIC. The interrupt
+ * controller subtypes in MADT of ACPI spec for RISC-V are defined in
+ * the incremental order like RINTC(24)->IMSIC(25)->APLIC(26)->PLIC(27).
+ * Hence, simply sorting the subtypes in incremental order will
+ * establish the required order.
+ */
+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);
+}
-- 
2.43.0