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[RFC,03/32] drivers: base: Use present CPUs in GENERIC_CPU_DEVICES

Message ID 20230203135043.409192-4-james.morse@arm.com
State Superseded
Headers show
Series ACPI/arm64: add support for virtual cpuhotplug | expand

Commit Message

James Morse Feb. 3, 2023, 1:50 p.m. UTC 
The four ACPI architectures only create sysfs entries using register_cpu()
for present CPUs, whereas GENERIC_CPU_DEVICES does this for possible CPUs.

Only two of the eight architectures that use GENERIC_CPU_DEVICES have a
distinction between present and possible CPUs.

To allow all four ACPI architectures to use GENERIC_CPU_DEVICES, change
it to use for_each_present_cpu().

The following architectures use GENERIC_CPU_DEVICES but are not SMP,
so possible == present:
 * m68k
 * microblaze
 * nios2

The following architectures use GENERIC_CPU_DEVICES and consider
possible == present:
 * csky: setup_smp()
 * hexagon: compare smp_start_cpus() and smp_prepare_cpus()
 * parisc: smp_prepare_boot_cpu() marks the boot cpu as present,
   processor_probe() sets possible for all CPUs and present for all CPUs
   except the boot cpu.

um appears to be a subarchitecture of x86.

The remaining architecture using GENERIC_CPU_DEVICES is openrisc,
where smp_init_cpus() makes all CPUs < NR_CPUS possible, whereas
smp_prepare_cpus() only makes CPUs < setup_max_cpus present. After this
change, openrisc systems that boot with max_cpus=1 would not see other
CPUs present in sysfs. This should not be a problem as these CPUs can't
be brought online as _cpu_up() checks cpu_present().

Signed-off-by: James Morse <james.morse@arm.com>
---
 drivers/base/cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c98849577d4..cf6407c34ede 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -500,7 +500,7 @@  static void __init cpu_dev_register_generic(void)
 #ifdef CONFIG_GENERIC_CPU_DEVICES
 	int i;
 
-	for_each_possible_cpu(i) {
+	for_each_present_cpu(i) {
 		if (register_cpu(&per_cpu(cpu_devices, i), i))
 			panic("Failed to register CPU device");
 	}