From 7fa22bd5460bb2021729fa5a1012c60b9b3a56e2 Mon Sep 17 00:00:00 2001 From: Stephen Boyd Date: Thu, 7 Jul 2011 01:56:51 +0100 Subject: ARM: 6993/1: platsmp: Allow secondary cpu hotplug with maxcpus=1 If an ARM system has multiple cpus in the same socket and the kernel is booted with maxcpus=1, secondary cpus are possible but not present due to how platform_smp_prepare_cpus() is called. Since most typical ARM processors don't actually support physical hotplug, initialize the present map to be equal to the possible map in generic ARM SMP code. Also, always call platform_smp_prepare_cpus() as long as max_cpus is non-zero (0 means no SMP) to allow platform code to do any SMP setup. After applying this patch it's possible to boot an ARM system with maxcpus=1 on the command line and then hotplug in secondary cpus via sysfs. This is more in line with how x86 does things. Signed-off-by: Stephen Boyd Cc: Paul Mundt Cc: Kukjin Kim Cc: David Brown Cc: Tony Lindgren Cc: Srinidhi Kasagar Cc: Linus Walleij Signed-off-by: Russell King --- arch/arm/kernel/smp.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'arch/arm/kernel/smp.c') diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 344e52b16c8c..0ffcf5c0da43 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -361,14 +361,21 @@ void __init smp_prepare_cpus(unsigned int max_cpus) */ if (max_cpus > ncores) max_cpus = ncores; - - if (max_cpus > 1) { + if (ncores > 1 && max_cpus) { /* * Enable the local timer or broadcast device for the * boot CPU, but only if we have more than one CPU. */ percpu_timer_setup(); + /* + * Initialise the present map, which describes the set of CPUs + * actually populated at the present time. A platform should + * re-initialize the map in platform_smp_prepare_cpus() if + * present != possible (e.g. physical hotplug). + */ + init_cpu_present(&cpu_possible_map); + /* * Initialise the SCU if there are more than one CPU * and let them know where to start. -- cgit v1.2.3