arm64: apple: CPU start driver

This driver is needed to spawn CPUs for SMP
on Apple Silicon platforms.

Apple Silicon doesn't have EL3, so PSCI isn't an option.

Signed-off-by: Stan Skowronek <stan@corellium.com>

Documentation/devicetree/bindings/arm/cpus.yaml

@@ -179,6 +179,7 @@ properties:
       - enum:
           - psci
           - spin-table
+          - apple
       # On ARM 32-bit systems this property is optional
       - enum:
           - actions,s500-smp

MAINTAINERS

@@ -1230,6 +1230,12 @@ L:	linux-input@vger.kernel.org
 S:	Odd fixes
 F:	drivers/input/mouse/bcm5974.c
 
+APPLE CPU START DRIVER
+M:	Stan Skowronek <stan@corellium.com>
+L:	linux-arm-kernel@lists.infradead.org
+S:	Maintained
+F:	arch/arm64/kernel/apple_cpustart.c
+
 APPLE SMC DRIVER
 M:	Henrik Rydberg <rydberg@bitmath.org>
 L:	linux-hwmon@vger.kernel.org

arch/arm64/kernel/Makefile

@@ -59,6 +59,7 @@ obj-$(CONFIG_CRASH_CORE)		+= crash_core.o
 obj-$(CONFIG_ARM_SDE_INTERFACE)		+= sdei.o
 obj-$(CONFIG_ARM64_PTR_AUTH)		+= pointer_auth.o
 obj-$(CONFIG_ARM64_MTE)			+= mte.o
+obj-$(CONFIG_ARCH_APPLE)		+= apple_cpustart.o
 
 obj-y					+= vdso/ probes/
 obj-$(CONFIG_COMPAT_VDSO)		+= vdso32/

arch/arm64/kernel/apple_cpustart.c

@@ -0,0 +1,153 @@
+/* SPDX-License-Identifier: (GPL-2.0 or BSD-3-Clause) */
+/*
+ * Copyright (C) 2020 Corellium LLC
+ */
+
+#include <linux/init.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/smp.h>
+#include <linux/delay.h>
+#include <linux/mm.h>
+
+#include <asm/cpu_ops.h>
+#include <asm/errno.h>
+#include <asm/smp_plat.h>
+#include <asm/io.h>
+
+#define MAGIC_UNLOCK 0xc5acce55
+
+struct cpu_apple_start_info {
+	void __iomem *pmgr_start;
+	u64 pmgr_start_size;
+	void __iomem *cputrc_rvbar;
+	void __iomem *dbg_unlock;
+};
+
+extern void apple_aic_cpu_prepare(unsigned int cpu);
+
+static int cpu_apple_start0_unlocked = 0;
+static DEFINE_PER_CPU(struct cpu_apple_start_info, cpu_apple_start_info);
+
+static int __init cpu_apple_start_init(unsigned int cpu)
+{
+	return 0;
+}
+
+static int cpu_apple_start_prepare(unsigned int cpu)
+{
+	struct device_node *node;
+	struct cpu_apple_start_info *info;
+
+	info = per_cpu_ptr(&cpu_apple_start_info, cpu);
+
+	if (info->pmgr_start && info->cputrc_rvbar && info->dbg_unlock)
+		return 0;
+
+	node = of_find_compatible_node(NULL, NULL, "apple,startcpu");
+	if (!node) {
+		pr_err("%s: missing startcpu node in device tree.\n", __func__);
+		return -EINVAL;
+	}
+
+	if (!info->pmgr_start) {
+		info->pmgr_start = of_iomap(node, cpu * 3);
+		if (!info->pmgr_start) {
+			pr_err("%s: failed to map start register for CPU %d.\n",
+			       __func__, cpu);
+			return -EINVAL;
+		}
+		if (!of_get_address(node, cpu * 3, &info->pmgr_start_size,
+				    NULL))
+			info->pmgr_start_size = 8;
+	}
+
+	if (!info->cputrc_rvbar) {
+		info->cputrc_rvbar = of_iomap(node, cpu * 3 + 1);
+		if (!info->cputrc_rvbar) {
+			pr_err("%s: failed to map reset address register for CPU %d.\n",
+			       __func__, cpu);
+			return -EINVAL;
+		}
+	}
+
+	if (!info->dbg_unlock) {
+		info->dbg_unlock = of_iomap(node, cpu * 3 + 2);
+		if (!info->dbg_unlock) {
+			pr_err("%s: failed to map unlock register for CPU %d.\n",
+			       __func__, cpu);
+			return -EINVAL;
+		}
+	}
+
+	if (cpu)
+		apple_aic_cpu_prepare(cpu);
+
+	return 0;
+}
+
+static int cpu_apple_start_boot(unsigned int cpu)
+{
+	struct cpu_apple_start_info *info;
+	unsigned long addr;
+
+	if (!cpu_apple_start0_unlocked) {
+		if (!cpu_apple_start_prepare(0)) {
+			info = per_cpu_ptr(&cpu_apple_start_info, 0);
+			writel(MAGIC_UNLOCK, info->dbg_unlock);
+			cpu_apple_start0_unlocked = 1;
+		} else
+			pr_err("%s: failed to unlock boot CPU\n", __func__);
+	}
+
+	info = per_cpu_ptr(&cpu_apple_start_info, cpu);
+
+	if (!info->pmgr_start || !info->cputrc_rvbar || !info->dbg_unlock)
+		return -EINVAL;
+
+	writeq(__pa_symbol(secondary_entry) | 1, info->cputrc_rvbar);
+	readq(info->cputrc_rvbar);
+	writeq(__pa_symbol(secondary_entry) | 1, info->cputrc_rvbar);
+	addr = readq(info->cputrc_rvbar) & 0xFFFFFFFFFul;
+	dsb(sy);
+
+	if (addr != (__pa_symbol(secondary_entry) | 1))
+		pr_err("%s: CPU%d reset address: 0x%lx, failed to set to 0x%lx.\n",
+		       __func__, cpu, addr,
+		       (unsigned long)(__pa_symbol(secondary_entry) | 1));
+
+	writel(MAGIC_UNLOCK, info->dbg_unlock);
+
+	writel(1 << cpu, info->pmgr_start);
+	if (info->pmgr_start_size >= 12) {
+		if (cpu < 4) {
+			writel(1 << cpu, info->pmgr_start + 4);
+			writel(0, info->pmgr_start + 8);
+		} else {
+			writel(0, info->pmgr_start + 4);
+			writel(1 << (cpu - 4), info->pmgr_start + 8);
+		}
+	} else
+		writel(1 << cpu, info->pmgr_start + 4);
+
+	dsb(sy);
+	sev();
+
+	return 0;
+}
+
+static void cpu_apple_wfi(void)
+{
+	/* can't do a proper WFI, because the CPU tends to lose state; will need
+       a proper wrapper sequence */
+	dsb(sy);
+	wfe();
+}
+
+const struct cpu_operations cpu_apple_start_ops = {
+	.name = "apple",
+	.cpu_init = cpu_apple_start_init,
+	.cpu_prepare = cpu_apple_start_prepare,
+	.cpu_boot = cpu_apple_start_boot,
+	.cpu_wfi = cpu_apple_wfi,
+};