powerpc/xmon: Exclude all of xmon from ftrace

Exclude core xmon files from ftrace (along with an xmon xive helper
outside of xmon/) to minimize impact of ftrace while within xmon.

Before:
  /sys/kernel/debug/tracing# grep -ci xmon available_filter_functions
  26

After:
  /sys/kernel/debug/tracing# grep -ci xmon available_filter_functions
  0
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
[mpe: Use $(subst ..) on KBUILD_CFLAGS rather than CFLAGS_REMOVE_xxx]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/xive/common.c

@@ -190,7 +190,7 @@ static u32 xive_scan_interrupts(struct xive_cpu *xc, bool just_peek)
  * This is used to perform the magic loads from an ESB
  * described in xive.h
  */
-static u8 xive_poke_esb(struct xive_irq_data *xd, u32 offset)
+static notrace u8 xive_poke_esb(struct xive_irq_data *xd, u32 offset)
 {
 	u64 val;
 
@@ -204,7 +204,7 @@ static u8 xive_poke_esb(struct xive_irq_data *xd, u32 offset)
 }
 
 #ifdef CONFIG_XMON
-static void xive_dump_eq(const char *name, struct xive_q *q)
+static notrace void xive_dump_eq(const char *name, struct xive_q *q)
 {
 	u32 i0, i1, idx;
 
@@ -218,7 +218,7 @@ static void xive_dump_eq(const char *name, struct xive_q *q)
 		    q->toggle, i0, i1);
 }
 
-void xmon_xive_do_dump(int cpu)
+notrace void xmon_xive_do_dump(int cpu)
 {
 	struct xive_cpu *xc = per_cpu(xive_cpu, cpu);
 

arch/powerpc/xmon/Makefile

@@ -5,6 +5,10 @@ subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror
 GCOV_PROFILE := n
 UBSAN_SANITIZE := n
 
+# Disable ftrace for the entire directory
+ORIG_CFLAGS := $(KBUILD_CFLAGS)
+KBUILD_CFLAGS = $(subst -mno-sched-epilog,,$(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS)))
+
 ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)
 
 obj-y			+= xmon.o nonstdio.o spr_access.o