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>

3 files changed, 59 insertions, 0 deletions

diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
index 22a3b9b5d4a1..772435b08207 100644
--- a/arch/arm/include/asm/smp.h
+++ b/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
  */
diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
index f751714d52c1..c7419a585ddc 100644
--- a/arch/arm/kernel/devtree.c
+++ b/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;
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index bc2121fa9132..bd02ca7a1d55 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/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()