menu "Boot options"
 
+config ARM64_ACPI_PARKING_PROTOCOL
+       bool "Enable support for the ARM64 ACPI parking protocol"
+       depends on ACPI
+       help
+         Enable support for the ARM64 ACPI parking protocol. If disabled
+         the kernel will not allow booting through the ARM64 ACPI parking
+         protocol even if the corresponding data is present in the ACPI
+         MADT table.
+
 config CMDLINE
        string "Default kernel command string"
        default ""
 
 static inline void acpi_init_cpus(void) { }
 #endif /* CONFIG_ACPI */
 
+#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
+bool acpi_parking_protocol_valid(int cpu);
+void __init
+acpi_set_mailbox_entry(int cpu, struct acpi_madt_generic_interrupt *processor);
+#else
+static inline bool acpi_parking_protocol_valid(int cpu) { return false; }
+static inline void
+acpi_set_mailbox_entry(int cpu, struct acpi_madt_generic_interrupt *processor)
+{}
+#endif
+
 static inline const char *acpi_get_enable_method(int cpu)
 {
-       return acpi_psci_present() ? "psci" : NULL;
+       if (acpi_psci_present())
+               return "psci";
+
+       if (acpi_parking_protocol_valid(cpu))
+               return "parking-protocol";
+
+       return NULL;
 }
 
 #ifdef CONFIG_ACPI_APEI
 
 #include <linux/threads.h>
 #include <asm/irq.h>
 
-#define NR_IPI 5
+#define NR_IPI 6
 
 typedef struct {
        unsigned int __softirq_pending;
 
 extern void arch_send_call_function_single_ipi(int cpu);
 extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
 
+#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
+extern void arch_send_wakeup_ipi_mask(const struct cpumask *mask);
+#else
+static inline void arch_send_wakeup_ipi_mask(const struct cpumask *mask)
+{
+       BUILD_BUG();
+}
+#endif
+
 extern int __cpu_disable(void);
 
 extern void __cpu_die(unsigned int cpu);
 
 arm64-obj-$(CONFIG_PCI)                        += pci.o
 arm64-obj-$(CONFIG_ARMV8_DEPRECATED)   += armv8_deprecated.o
 arm64-obj-$(CONFIG_ACPI)               += acpi.o
+arm64-obj-$(CONFIG_ARM64_ACPI_PARKING_PROTOCOL)        += acpi_parking_protocol.o
 arm64-obj-$(CONFIG_PARAVIRT)           += paravirt.o
 
 obj-y                                  += $(arm64-obj-y) vdso/
 
--- /dev/null
+/*
+ * ARM64 ACPI Parking Protocol implementation
+ *
+ * Authors: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
+ *         Mark Salter <msalter@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <linux/acpi.h>
+#include <linux/types.h>
+
+#include <asm/cpu_ops.h>
+
+struct cpu_mailbox_entry {
+       phys_addr_t mailbox_addr;
+       u8 version;
+       u8 gic_cpu_id;
+};
+
+static struct cpu_mailbox_entry cpu_mailbox_entries[NR_CPUS];
+
+void __init acpi_set_mailbox_entry(int cpu,
+                                  struct acpi_madt_generic_interrupt *p)
+{
+       struct cpu_mailbox_entry *cpu_entry = &cpu_mailbox_entries[cpu];
+
+       cpu_entry->mailbox_addr = p->parked_address;
+       cpu_entry->version = p->parking_version;
+       cpu_entry->gic_cpu_id = p->cpu_interface_number;
+}
+
+bool acpi_parking_protocol_valid(int cpu)
+{
+       struct cpu_mailbox_entry *cpu_entry = &cpu_mailbox_entries[cpu];
+
+       return cpu_entry->mailbox_addr && cpu_entry->version;
+}
+
+static int acpi_parking_protocol_cpu_init(unsigned int cpu)
+{
+       pr_debug("%s: ACPI parked addr=%llx\n", __func__,
+                 cpu_mailbox_entries[cpu].mailbox_addr);
+
+       return 0;
+}
+
+static int acpi_parking_protocol_cpu_prepare(unsigned int cpu)
+{
+       return 0;
+}
+
+struct parking_protocol_mailbox {
+       __le32 cpu_id;
+       __le32 reserved;
+       __le64 entry_point;
+};
+
+static int acpi_parking_protocol_cpu_boot(unsigned int cpu)
+{
+       struct cpu_mailbox_entry *cpu_entry = &cpu_mailbox_entries[cpu];
+       struct parking_protocol_mailbox __iomem *mailbox;
+       __le32 cpu_id;
+
+       /*
+        * Map mailbox memory with attribute device nGnRE (ie ioremap -
+        * this deviates from the parking protocol specifications since
+        * the mailboxes are required to be mapped nGnRnE; the attribute
+        * discrepancy is harmless insofar as the protocol specification
+        * is concerned).
+        * If the mailbox is mistakenly allocated in the linear mapping
+        * by FW ioremap will fail since the mapping will be prevented
+        * by the kernel (it clashes with the linear mapping attributes
+        * specifications).
+        */
+       mailbox = ioremap(cpu_entry->mailbox_addr, sizeof(*mailbox));
+       if (!mailbox)
+               return -EIO;
+
+       cpu_id = readl_relaxed(&mailbox->cpu_id);
+       /*
+        * Check if firmware has set-up the mailbox entry properly
+        * before kickstarting the respective cpu.
+        */
+       if (cpu_id != ~0U) {
+               iounmap(mailbox);
+               return -ENXIO;
+       }
+
+       /*
+        * We write the entry point and cpu id as LE regardless of the
+        * native endianness of the kernel. Therefore, any boot-loaders
+        * that read this address need to convert this address to the
+        * Boot-Loader's endianness before jumping.
+        */
+       writeq_relaxed(__pa(secondary_entry), &mailbox->entry_point);
+       writel_relaxed(cpu_entry->gic_cpu_id, &mailbox->cpu_id);
+
+       arch_send_wakeup_ipi_mask(cpumask_of(cpu));
+
+       iounmap(mailbox);
+
+       return 0;
+}
+
+static void acpi_parking_protocol_cpu_postboot(void)
+{
+       int cpu = smp_processor_id();
+       struct cpu_mailbox_entry *cpu_entry = &cpu_mailbox_entries[cpu];
+       struct parking_protocol_mailbox __iomem *mailbox;
+       __le64 entry_point;
+
+       /*
+        * Map mailbox memory with attribute device nGnRE (ie ioremap -
+        * this deviates from the parking protocol specifications since
+        * the mailboxes are required to be mapped nGnRnE; the attribute
+        * discrepancy is harmless insofar as the protocol specification
+        * is concerned).
+        * If the mailbox is mistakenly allocated in the linear mapping
+        * by FW ioremap will fail since the mapping will be prevented
+        * by the kernel (it clashes with the linear mapping attributes
+        * specifications).
+        */
+       mailbox = ioremap(cpu_entry->mailbox_addr, sizeof(*mailbox));
+       if (!mailbox)
+               return;
+
+       entry_point = readl_relaxed(&mailbox->entry_point);
+       /*
+        * Check if firmware has cleared the entry_point as expected
+        * by the protocol specification.
+        */
+       WARN_ON(entry_point);
+
+       iounmap(mailbox);
+}
+
+const struct cpu_operations acpi_parking_protocol_ops = {
+       .name           = "parking-protocol",
+       .cpu_init       = acpi_parking_protocol_cpu_init,
+       .cpu_prepare    = acpi_parking_protocol_cpu_prepare,
+       .cpu_boot       = acpi_parking_protocol_cpu_boot,
+       .cpu_postboot   = acpi_parking_protocol_cpu_postboot
+};
 
 #include <asm/smp_plat.h>
 
 extern const struct cpu_operations smp_spin_table_ops;
+extern const struct cpu_operations acpi_parking_protocol_ops;
 extern const struct cpu_operations cpu_psci_ops;
 
 const struct cpu_operations *cpu_ops[NR_CPUS];
 
-static const struct cpu_operations *supported_cpu_ops[] __initconst = {
+static const struct cpu_operations *dt_supported_cpu_ops[] __initconst = {
        &smp_spin_table_ops,
        &cpu_psci_ops,
        NULL,
 };
 
+static const struct cpu_operations *acpi_supported_cpu_ops[] __initconst = {
+#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
+       &acpi_parking_protocol_ops,
+#endif
+       &cpu_psci_ops,
+       NULL,
+};
+
 static const struct cpu_operations * __init cpu_get_ops(const char *name)
 {
-       const struct cpu_operations **ops = supported_cpu_ops;
+       const struct cpu_operations **ops;
+
+       ops = acpi_disabled ? dt_supported_cpu_ops : acpi_supported_cpu_ops;
 
        while (*ops) {
                if (!strcmp(name, (*ops)->name))
                }
        } else {
                enable_method = acpi_get_enable_method(cpu);
-               if (!enable_method)
-                       pr_err("Unsupported ACPI enable-method\n");
+               if (!enable_method) {
+                       /*
+                        * In ACPI systems the boot CPU does not require
+                        * checking the enable method since for some
+                        * boot protocol (ie parking protocol) it need not
+                        * be initialized. Don't warn spuriously.
+                        */
+                       if (cpu != 0)
+                               pr_err("Unsupported ACPI enable-method\n");
+               }
        }
 
        return enable_method;
 
        IPI_CPU_STOP,
        IPI_TIMER,
        IPI_IRQ_WORK,
+       IPI_WAKEUP
 };
 
 /*
        /* map the logical cpu id to cpu MPIDR */
        cpu_logical_map(cpu_count) = hwid;
 
+       /*
+        * Set-up the ACPI parking protocol cpu entries
+        * while initializing the cpu_logical_map to
+        * avoid parsing MADT entries multiple times for
+        * nothing (ie a valid cpu_logical_map entry should
+        * contain a valid parking protocol data set to
+        * initialize the cpu if the parking protocol is
+        * the only available enable method).
+        */
+       acpi_set_mailbox_entry(cpu_count, processor);
+
        cpu_count++;
 }
 
        S(IPI_CPU_STOP, "CPU stop interrupts"),
        S(IPI_TIMER, "Timer broadcast interrupts"),
        S(IPI_IRQ_WORK, "IRQ work interrupts"),
+       S(IPI_WAKEUP, "CPU wake-up interrupts"),
 };
 
 static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
        smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC);
 }
 
+#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
+void arch_send_wakeup_ipi_mask(const struct cpumask *mask)
+{
+       smp_cross_call(mask, IPI_WAKEUP);
+}
+#endif
+
 #ifdef CONFIG_IRQ_WORK
 void arch_irq_work_raise(void)
 {
                break;
 #endif
 
+#ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
+       case IPI_WAKEUP:
+               WARN_ONCE(!acpi_parking_protocol_valid(cpu),
+                         "CPU%u: Wake-up IPI outside the ACPI parking protocol\n",
+                         cpu);
+               break;
+#endif
+
        default:
                pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
                break;