On Fri, Aug 05, 2016 at 05:50:29PM +1000, David Gibson wrote: > Prior to c8721d3 "spapr: Error out when CPU hotplug is attempted on older > pseries machines", attempting to use query-hotpluggable-cpus on pseries-2.6 > and earlier machine types would SEGV. > > That change fixed that, but due to some unexpected interactions in init > order and a brown-paper-bag worthy failure to test, it accidentally > disabled query-hotpluggable-cpus for all pseries machine types, including > the current one which should allow it. > > In fact, query_hotpluggable_cpus needs to be non-NULL when and only when > the dr_cpu_enabled flag in sPAPRMachineClass is set, which makes > dr_cpu_enabled itself redundant. > > This patch removes dr_cpu_enabled, instead directly setting > query_hotpluggable_cpus from the machine class_init functions, and using > that to determine the availability of CPU hotplug when necessary.
dr_cpu_enabled actually determines if CPU hotplug feature is present or not. It also controls the creation of DRC-specific properties in /cpus DT node like ibm,drc-indexes etc query_hotpluggable_cpus just tells us if the machine supports the querying of hotpluggable CPUS. query_hotpluggable_cpus definitely implies dr_cpu_enabled but dr_cpu_enabled can exist on its own (theoretically at the least) without query_hotpluggable_cpus. So I think we should not replace dr_cpu_enabled with query_hotpluggable_cpus. However, I tested this patch and it works as intended. Regards, Bharata.
