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Message-ID: <20140108150612.GC11753@e106331-lin.cambridge.arm.com>
Date: Wed, 8 Jan 2014 15:06:12 +0000
From: Mark Rutland <mark.rutland@....com>
To: Stephen Boyd <sboyd@...eaurora.org>
Cc: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
David Brown <davidb@...eaurora.org>,
Rohit Vaswani <rvaswani@...eaurora.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
Kumar Gala <galak@...eaurora.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH v2 4/9] ARM: Introduce CPU_METHOD_OF_DECLARE() for cpu
hotplug/smp
On Tue, Dec 24, 2013 at 12:39:48AM +0000, Stephen Boyd wrote:
> 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.
Nice!
>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Russell King <linux@....linux.org.uk>
> Cc: <devicetree@...r.kernel.org>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
> arch/arm/include/asm/smp.h | 9 +++++++++
> arch/arm/kernel/devtree.c | 40 +++++++++++++++++++++++++++++++++++++++
> include/asm-generic/vmlinux.lds.h | 10 ++++++++++
> 3 files changed, 59 insertions(+)
>
> diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
> index 22a3b9b..772435b 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 739c3df..91cc3f8 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
I was going to comment that this would look nicer using an error code or
0, rather than 0 or 1, but I see that would make the call sites more
complicated / less legible.
> +
> +
> /*
> * 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 bc2121f..bd02ca7 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
I suspect we'll use this on arm64 in future, where we might need this
even on UP systems (for PSCI's cpu_suspend method). However, I think
that can change that as and when we require it.
> +
> #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()
Enthusiastically Acked-by: Mark Rutland <mark.rutland@....com>
Cheers,
Mark.
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