On Thu, 14 Sep 2023 15:07:22 +0100 "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx> wrote: > On Thu, Sep 14, 2023 at 12:27:15PM +0100, Jonathan Cameron wrote: > > On Wed, 13 Sep 2023 16:37:54 +0000 > > James Morse <james.morse@xxxxxxx> wrote: > > > > > To allow ACPI's _STA value to hide CPUs that are present, but not > > > available to online right now due to VMM or firmware policy, the > > > register_cpu() call needs to be made by the ACPI machinery when ACPI > > > is in use. This allows it to hide CPUs that are unavailable from sysfs. > > > > > > Switching to GENERIC_CPU_DEVICES is an intermediate step to allow all > > > five ACPI architectures to be modified at once. > > > > > > Switch over to GENERIC_CPU_DEVICES, and provide an arch_register_cpu() > > > that populates the hotpluggable flag. arch_register_cpu() is also the > > > interface the ACPI machinery expects. > > > > > > The struct cpu in struct cpuinfo_arm64 is never used directly, remove > > > it to use the one GENERIC_CPU_DEVICES provides. > > > > > > This changes the CPUs visible in sysfs from possible to present, but > > > on arm64 smp_prepare_cpus() ensures these are the same. > > > > > > Signed-off-by: James Morse <james.morse@xxxxxxx> > > > > After this the earlier question about ordering of cpu_dev_init() > > and node_dev_init() is relevant. > > > > Why won't node_dev_init() call > > get_cpu_devce() which queries per_cpu(cpu_sys_devices) > > and get NULL as we haven't yet filled that in? > > > > Or does it do so but that doesn't matter as well create the > > relevant links later? > > node_dev_init() will walk through the nodes calling register_one_node() > on each. This will trickle down to __register_one_node() which walks > all present CPUs, calling register_cpu_under_node() on each. > > register_cpu_under_node() will call get_cpu_device(cpu) for each and > will return NULL until the CPU is registered using register_cpu(), > which will now happen _after_ node_dev_init(). > > So, at this point, CPUs won't get registered, and initially one might > think that's a problem. > > However, register_cpu() will itself call register_cpu_under_node(), > where get_cpu_device() will return the now populated entry, and the > sysfs links will be created. > > So, I think what you've spotted is a potential chunk of code that > isn't necessary when using GENERIC_CPU_DEVICES after this change! > Makes sense thanks. I was just being too lazy to check and bouncing it back at James! *looks guilty* Jonathan
