arm64: kernel: implement ACPI parking protocol

The SBBR and ACPI specifications allow ACPI based systems that do not
implement PSCI (eg systems with no EL3) to boot through the ACPI parking
protocol specification[1].

This patch implements the ACPI parking protocol CPU operations, and adds
code that eases parsing the parking protocol data structures to the
ARM64 SMP initializion carried out at the same time as cpus enumeration.

To wake-up the CPUs from the parked state, this patch implements a
wakeup IPI for ARM64 (ie arch_send_wakeup_ipi_mask()) that mirrors the
ARM one, so that a specific IPI is sent for wake-up purpose in order
to distinguish it from other IPI sources.

Given the current ACPI MADT parsing API, the patch implements a glue
layer that helps passing MADT GICC data structure from SMP initialization
code to the parking protocol implementation somewhat overriding the CPU
operations interfaces. This to avoid creating a completely trasparent
DT/ACPI CPU operations layer that would require creating opaque
structure handling for CPUs data (DT represents CPU through DT nodes, ACPI
through static MADT table entries), which seems overkill given that ACPI
on ARM64 mandates only two booting protocols (PSCI and parking protocol),
so there is no need for further protocol additions.

Based on the original work by Mark Salter <[e-mail]>

[1] https://acpica.org/sites/acpica/files/MP%20Startup%20for%20ARM%20platforms.docx

Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Tested-by: Loc Ho <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Hanjun Guo <[e-mail]>
Cc: Sudeep Holla <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Mark Salter <[e-mail]>
Cc: Al Stone <[e-mail]>
[[e-mail]: Added WARN_ONCE(!acpi_parking_protocol_valid() on the IPI]
Signed-off-by: Catalin Marinas <[e-mail]>

arch/arm64/Kconfig

···
 
 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 ""

arch/arm64/include/asm/acpi.h

···
 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

arch/arm64/include/asm/hardirq.h

···
 #include <linux/threads.h>
 #include <asm/irq.h>
 
-#define NR_IPI	5
+#define NR_IPI	6
 
 typedef struct {
 	unsigned int __softirq_pending;

arch/arm64/include/asm/smp.h

···
 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);

arch/arm64/kernel/Makefile

···
 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/

arch/arm64/kernel/acpi_parking_protocol.c

···
+/*
+ * ARM64 ACPI Parking Protocol implementation
+ *
+ * Authors: Lorenzo Pieralisi <[e-mail]>
+ *	    Mark Salter <[e-mail]>
+ *
+ * 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
+};

arch/arm64/kernel/cpu_ops.c

···
 #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;

arch/arm64/kernel/smp.c

···
 	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)
···
 		irq_enter();
 		irq_work_run();
 		irq_exit();
+		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