Make PFAIR optional to prevent build and runtime failures.

The PFAIR plugin always implicitly assumed !NO_HZ (the schedule
is wrong if NO_HZ is enabled) and does not built if hrtimers are absent:

> litmus/built-in.o: In function `pfair_activate_plugin':
> sched_pfair.c:(.text+0x7f07): undefined reference to `cpu_stagger_offset'
> litmus/built-in.o: In function `init_pfair':
> sched_pfair.c:(.init.text+0x487): undefined reference to `cpu_stagger_offset'

cpu_stagger_offset() is only available if hrtimers are enabled.

This patch makes these dependencies explicit.

1 files changed, 2 insertions, 2 deletions

diff --git a/litmus/Makefile b/litmus/Makefile
index e581e87213c2..30369787ece2 100644
--- a/litmus/Makefile
+++ b/litmus/Makefile
@@ -13,10 +13,10 @@ obj-y     = sched_plugin.o litmus.o \
             bheap.o \
             ctrldev.o \
             sched_gsn_edf.o \
-            sched_psn_edf.o \
-            sched_pfair.o
+            sched_psn_edf.o
 
 obj-$(CONFIG_PLUGIN_CEDF) += sched_cedf.o
+obj-$(CONFIG_PLUGIN_PFAIR) += sched_pfair.o
 
 obj-$(CONFIG_FEATHER_TRACE) += ft_event.o ftdev.o
 obj-$(CONFIG_SCHED_TASK_TRACE) += sched_task_trace.o