ARM: Introduce CPU_METHOD_OF_DECLARE() for cpu hotplug/smp

The goal of multi-platform kernels is to remove the need for mach
directories and machine descriptors. To further that goal,
introduce CPU_METHOD_OF_DECLARE() to allow cpu hotplug/smp
support to be separated from the machine descriptors.
Implementers should specify an enable-method property in their
cpus node and then implement a matching set of smp_ops in their
hotplug/smp code, wiring it up with the CPU_METHOD_OF_DECLARE()
macro. When the kernel is compiled we'll collect all the
enable-method smp_ops into one section for use at boot.

At boot time we'll look for an enable-method in each cpu node and
try to match that against all known CPU enable methods in the
kernel. If there are no enable-methods in the cpu nodes we
fallback to the cpus node and try to use any enable-method found
there. If that doesn't work we fall back to the old way of using
the machine descriptor.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: <devicetree@vger.kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kumar Gala <galak@codeaurora.org>

arch/arm/include/asm/smp.h

@@ -114,6 +114,15 @@ struct smp_operations {
 #endif
 };
 
+struct of_cpu_method {
+	const char *method;
+	struct smp_operations *ops;
+};
+
+#define CPU_METHOD_OF_DECLARE(name, _method, _ops)			\
+	static const struct of_cpu_method __cpu_method_of_table_##name	\
+		__used __section(__cpu_method_of_table)			\
+		= { .method = _method, .ops = _ops }
 /*
  * set platform specific SMP operations
  */

arch/arm/kernel/devtree.c

@@ -18,6 +18,7 @@
 #include <linux/of_fdt.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
+#include <linux/smp.h>
 
 #include <asm/cputype.h>
 #include <asm/setup.h>
@@ -63,6 +64,34 @@ void __init arm_dt_memblock_reserve(void)
 	}
 }
 
+#ifdef CONFIG_SMP
+extern struct of_cpu_method __cpu_method_of_table_begin[];
+extern struct of_cpu_method __cpu_method_of_table_end[];
+
+static int __init set_smp_ops_by_method(struct device_node *node)
+{
+	const char *method;
+	struct of_cpu_method *m = __cpu_method_of_table_begin;
+
+	if (of_property_read_string(node, "enable-method", &method))
+		return 0;
+
+	for (; m < __cpu_method_of_table_end; m++)
+		if (!strcmp(m->method, method)) {
+			smp_set_ops(m->ops);
+			return 1;
+		}
+
+	return 0;
+}
+#else
+static inline int set_smp_ops_by_method(struct device_node *node)
+{
+	return 1;
+}
+#endif
+
+
 /*
  * arm_dt_init_cpu_maps - Function retrieves cpu nodes from the device tree
  * and builds the cpu logical map array containing MPIDR values related to
@@ -79,6 +108,7 @@ void __init arm_dt_init_cpu_maps(void)
 	 * read as 0.
 	 */
 	struct device_node *cpu, *cpus;
+	int found_method = 0;
 	u32 i, j, cpuidx = 1;
 	u32 mpidr = is_smp() ? read_cpuid_mpidr() & MPIDR_HWID_BITMASK : 0;
 
@@ -150,8 +180,18 @@ void __init arm_dt_init_cpu_maps(void)
 		}
 
 		tmp_map[i] = hwid;
+
+		if (!found_method)
+			found_method = set_smp_ops_by_method(cpu);
 	}
 
+	/*
+	 * Fallback to an enable-method in the cpus node if nothing found in
+	 * a cpu node.
+	 */
+	if (!found_method)
+		set_smp_ops_by_method(cpus);
+
 	if (!bootcpu_valid) {
 		pr_warn("DT missing boot CPU MPIDR[23:0], fall back to default cpu_logical_map\n");
 		return;

include/asm-generic/vmlinux.lds.h

@@ -167,6 +167,15 @@
 #define CLK_OF_TABLES()
 #endif
 
+#ifdef CONFIG_SMP
+#define CPU_METHOD_OF_TABLES() . = ALIGN(8);				    \
+			   VMLINUX_SYMBOL(__cpu_method_of_table_begin) = .; \
+			   *(__cpu_method_of_table)			    \
+			   VMLINUX_SYMBOL(__cpu_method_of_table_end) = .;
+#else
+#define CPU_METHOD_OF_TABLES()
+#endif
+
 #define KERNEL_DTB()							\
 	STRUCT_ALIGN();							\
 	VMLINUX_SYMBOL(__dtb_start) = .;				\
@@ -491,6 +500,7 @@
 	MEM_DISCARD(init.rodata)					\
 	CLK_OF_TABLES()							\
 	CLKSRC_OF_TABLES()						\
+	CPU_METHOD_OF_TABLES()						\
 	KERNEL_DTB()							\
 	IRQCHIP_OF_MATCH_TABLE()