[PATCH v2 4/6] PM / Hibernate: Allow architectures to specify the hibernate/resume CPU

[James Morse <james.morse@arm.com>]

On arm64 the cpu with logical id 0 is assumed to be the boot CPU. If a
user hotplugs this CPU out, then uses kexec to boot a new kernel, the new
kernel will assign logical id 0 to a different physical CPU.
This breaks hibernate as hibernate and resume will be attempted on different
CPUs.

Define a weak symbol arch_hibernation_disable_cpus(), which defaults to
calling disable_nonboot_cpus). Architectures that allow CPU 0 to be
hotplugged can use this to control which CPU is used for hibernate/resume.

Signed-off-by: James Morse <james.morse@arm.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Pavel Machek <pavel@ucw.cz>
---
If this approach is acceptable, this patch should go with 4&5 via the arm64
tree.

 kernel/power/hibernate.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index fca9254280ee..0e668a3207ec 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -70,6 +70,16 @@ bool hibernation_available(void)
 }
 
 /**
+ * arch_hibernation_disable_cpus - Allow architectures to direct which CPU
+ * is used for suspend or resume.
+ * @suspend: True during hibernate, false for resume.
+ */
+int __weak arch_hibernation_disable_cpus(__maybe_unused bool suspend)
+{
+	return disable_nonboot_cpus();
+}
+
+/**
  * hibernation_set_ops - Set the global hibernate operations.
  * @ops: Hibernation operations to use in subsequent hibernation transitions.
  */
@@ -279,7 +289,7 @@ static int create_image(int platform_mode)
 	if (error || hibernation_test(TEST_PLATFORM))
 		goto Platform_finish;
 
-	error = disable_nonboot_cpus();
+	error = arch_hibernation_disable_cpus(true);
 	if (error || hibernation_test(TEST_CPUS))
 		goto Enable_cpus;
 
@@ -433,7 +443,7 @@ static int resume_target_kernel(bool platform_mode)
 	if (error)
 		goto Cleanup;
 
-	error = disable_nonboot_cpus();
+	error = arch_hibernation_disable_cpus(false);
 	if (error)
 		goto Enable_cpus;
 
@@ -551,7 +561,7 @@ int hibernation_platform_enter(void)
 	if (error)
 		goto Platform_finish;
 
-	error = disable_nonboot_cpus();
+	error = arch_hibernation_disable_cpus(true);
 	if (error)
 		goto Enable_cpus;
 
-- 
2.8.0.rc3