Hi Stephen,
On Fri, Feb 13, 2015 at 10:06:39AM -0800, Stephen Boyd wrote:
> Writes to /sys/.../cpuX/online fail if we determine the platform
> doesn't support hotplug for that CPU. Furthermore, if the cpu_die
> op isn't specified the system hangs when we try to offline a CPU
> and it comes right back online unexpectedly. Let's figure this
> stuff out before we make the sysfs nodes so that the online file
> doesn't even exist if it isn't (at least sometimes) possible to
> hotplug the CPU.
>
> We re-purpose the cpu_disable smp op here and rename it to
> cpu_can_disable because all users use the op to indicate if a CPU
> can be hotplugged or not in a static fashion. With PSCI we may
> need to reintroduce the cpu_disable op so that the secure OS can
> be migrated off the CPU we're trying to hotplug. We'll need to
> indicate that all CPUs are hotpluggable in that case but this
> shouldn't be any worse than something like x86 where we indicate
> that all CPUs are hotpluggable but occasionally we can't offline
> a CPU due to check_irq_vectors_for_cpu_disable().
>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Nicolas Pitre <n...@linaro.org>
> Cc: Dave Martin <dave.mar...@arm.com>
> Cc: Simon Horman <ho...@verge.net.au>
> Cc: Magnus Damm <magnus.d...@gmail.com>
> Cc: <linux...@vger.kernel.org>
> Signed-off-by: Stephen Boyd <sb...@codeaurora.org>
[snip]
> diff --git a/arch/arm/mach-shmobile/platsmp.c
> b/arch/arm/mach-shmobile/platsmp.c
> index 3923e09e966d..a614cef18db1 100644
> --- a/arch/arm/mach-shmobile/platsmp.c
> +++ b/arch/arm/mach-shmobile/platsmp.c
> @@ -31,8 +31,8 @@ void shmobile_smp_hook(unsigned int cpu, unsigned long fn,
> unsigned long arg)
> }
>
> #ifdef CONFIG_HOTPLUG_CPU
> -int shmobile_smp_cpu_disable(unsigned int cpu)
> +int shmobile_smp_cpu_can_disable(unsigned int cpu)
> {
> - return 0; /* Hotplug of any CPU is supported */
> + return 1; /* Hotplug of any CPU is supported */
> }
> #endif
> diff --git a/arch/arm/mach-shmobile/smp-r8a7779.c
> b/arch/arm/mach-shmobile/smp-r8a7779.c
> index 3f761f839043..b45206f93ddf 100644
> --- a/arch/arm/mach-shmobile/smp-r8a7779.c
> +++ b/arch/arm/mach-shmobile/smp-r8a7779.c
> @@ -124,19 +124,12 @@ static int r8a7779_cpu_kill(unsigned int cpu)
>
> return 0;
> }
> -
> -static int r8a7779_cpu_disable(unsigned int cpu)
> -{
> - /* only CPU1->3 have power domains, do not allow hotplug of CPU0 */
> - return cpu == 0 ? -EPERM : 0;
> -}
> #endif /* CONFIG_HOTPLUG_CPU */
>
> struct smp_operations r8a7779_smp_ops __initdata = {
> .smp_prepare_cpus = r8a7779_smp_prepare_cpus,
> .smp_boot_secondary = r8a7779_boot_secondary,
> #ifdef CONFIG_HOTPLUG_CPU
> - .cpu_disable = r8a7779_cpu_disable,
> .cpu_die = shmobile_smp_scu_cpu_die,
> .cpu_kill = r8a7779_cpu_kill,
> #endif
Its not clear to me why r8a7779_cpu_disable() has been
removed rather than replaced by r8a7779_cpu_can_disable()
--
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