drivers/cpu: Add generic armv8 cpu driver

Add a generic driver that binds to armv8 CPU nodes. The generic driver allows
- to enumerate CPUs present in a system, even when no other driver binds it
- generates ACPI SSDT code for each CPU
- Fill the ACPI MADT table (implemented in a follow up patch)

The newly introduced code could also be reused on other CPU drivers that are
compatible with armv8.

TEST: Booted on QEMU sbsa and verify the driver binds to CPU nodes.
      Confirmed with FWTS that all ACPI processor devices are present.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>

drivers/cpu/Kconfig

@@ -26,6 +26,12 @@ config CPU_RISCV
 	help
 	  Support CPU cores for RISC-V architecture.
 
+config CPU_ARMV8
+	bool "Enable generic ARMv8 CPU driver"
+	depends on CPU && ARM64
+	help
+	  Support CPU cores for armv8 architecture.
+
 config CPU_MICROBLAZE
 	bool "Enable Microblaze CPU driver"
 	depends on CPU && MICROBLAZE

drivers/cpu/Makefile

@@ -6,10 +6,12 @@
 
 obj-$(CONFIG_CPU) += cpu-uclass.o
 
+
 obj-$(CONFIG_ARCH_BMIPS) += bmips_cpu.o
 obj-$(CONFIG_ARCH_IMX8) += imx8_cpu.o
 obj-$(CONFIG_ARCH_AT91) += at91_cpu.o
 obj-$(CONFIG_ARCH_MEDIATEK) += mtk_cpu.o
+obj-$(CONFIG_CPU_ARMV8) += armv8_cpu.o
 obj-$(CONFIG_CPU_IMX) += imx8_cpu.o
 obj-$(CONFIG_CPU_MPC83XX) += mpc83xx_cpu.o
 obj-$(CONFIG_CPU_RISCV) += riscv_cpu.o

drivers/cpu/armv8_cpu.c

@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2024 9elements GmbH
+ */
+#include <cpu.h>
+#include <dm.h>
+#include <acpi/acpigen.h>
+#include <asm/armv8/cpu.h>
+#include <dm/acpi.h>
+#include <asm/io.h>
+#include <linux/bitops.h>
+#include <linux/printk.h>
+#include <linux/sizes.h>
+
+static int armv8_cpu_get_desc(const struct udevice *dev, char *buf, int size)
+{
+	int cpuid;
+
+	cpuid = (read_midr() & MIDR_PARTNUM_MASK) >> MIDR_PARTNUM_SHIFT;
+
+	snprintf(buf, size, "CPU MIDR %04x", cpuid);
+
+	return 0;
+}
+
+static int armv8_cpu_get_info(const struct udevice *dev,
+			      struct cpu_info *info)
+{
+	info->cpu_freq = 0;
+	info->features = BIT(CPU_FEAT_L1_CACHE) | BIT(CPU_FEAT_MMU);
+
+	return 0;
+}
+
+static int armv8_cpu_get_count(const struct udevice *dev)
+{
+	return uclass_id_count(UCLASS_CPU);
+}
+
+#ifdef CONFIG_ACPIGEN
+int armv8_cpu_fill_ssdt(const struct udevice *dev, struct acpi_ctx *ctx)
+{
+	uint core_id = dev_seq(dev);
+
+	acpigen_write_processor_device(ctx, core_id);
+
+	return 0;
+}
+
+struct acpi_ops armv8_cpu_acpi_ops = {
+	.fill_ssdt	= armv8_cpu_fill_ssdt,
+};
+#endif
+
+static const struct cpu_ops cpu_ops = {
+	.get_count = armv8_cpu_get_count,
+	.get_desc  = armv8_cpu_get_desc,
+	.get_info  = armv8_cpu_get_info,
+};
+
+static const struct udevice_id cpu_ids[] = {
+	{ .compatible = "arm,armv8" },
+	{}
+};
+
+U_BOOT_DRIVER(arm_cpu) = {
+	.name		= "arm-cpu",
+	.id		= UCLASS_CPU,
+	.of_match	= cpu_ids,
+	.ops		= &cpu_ops,
+	.flags		= DM_FLAG_PRE_RELOC,
+	ACPI_OPS_PTR(&armv8_cpu_acpi_ops)
+};

drivers/cpu/armv8_cpu.h

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2024 9elements GmbH
+ */
+#include <dm/acpi.h>
+#include <dm/device.h>
+
+#ifndef _ARMV8_CPU_H_
+#define _ARMV8_CPU_H_
+
+/**
+ * armv8_cpu_fill_ssdt() - Fill the SSDT
+ * Parses the FDT and writes the SSDT nodes.
+ *
+ * @dev: cpu device to generate ACPI tables for
+ * @ctx: ACPI context pointer
+ * @return:	0 if OK, or a negative error code.
+ */
+int armv8_cpu_fill_ssdt(const struct udevice *dev, struct acpi_ctx *ctx);
+
+#endif