This code was until recently completely undocumented and even now the comment is
not very verbose.
We've already had one patch sent to remove the IRQ enable/disable because it's
"paradoxical and unnecessary". So document it thoroughly to save anyone else
from puzzling over it.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
/* Update affinity of all IRQs previously aimed at this CPU */
irq_migrate_all_off_this_cpu();
- /* Give the CPU time to drain in-flight ones */
+ /*
+ * Depending on the details of the interrupt controller, it's possible
+ * that one of the interrupts we just migrated away from this CPU is
+ * actually already pending on this CPU. If we leave it in that state
+ * the interrupt will never be EOI'ed, and will never fire again. So
+ * temporarily enable interrupts here, to allow any pending interrupt to
+ * be received (and EOI'ed), before we take this CPU offline.
+ */
local_irq_enable();
mdelay(1);
local_irq_disable();