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! -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
