clocksource/drivers/exynos_mct: Use container_of() instead of this_cpu_ptr()

Since evt structure is embedded in per-CPU mevt structure it's
definitely faster to use container_of() to get access to mevt
if we have evt (for example as incoming function argument) instead
of more expensive approach with this_cpu_ptr(&percpu_mct_tick).
this_cpu_ptr() on per-CPU mevt structure leads to access to cp15
to get cpu id and arithmetic operations.
Container_of() is cheaper since it's just one asm instruction.
This should work if used evt pointer is correct and owned by
local mevt structure.

For example, before this patch set_state_shutdown() looks like:

4a4: e92d4010 push {r4, lr}
4a8: e3004000 movw r4, #0
4ac: ebfffffe bl 0 <debug_smp_processor_id>
4b0: e3003000 movw r3, #0
4b4: e3404000 movt r4, #0
4b8: e3403000 movt r3, #0
4bc: e7933100 ldr r3, [r3, r0, lsl #2]
4c0: e0844003 add r4, r4, r3
4c4: e59400c0 ldr r0, [r4, #192] ; 0xc0
4c8: ebffffd4 bl 420 <exynos4_mct_tick_stop.isra.1>
4cc: e3a00000 mov r0, #0
4d0: e8bd8010 pop {r4, pc}

With this patch:

4a4: e92d4010 push {r4, lr}
4a8: e59000c0 ldr r0, [r0, #192] ; 0xc0
4ac: ebffffdb bl 420 <exynos4_mct_tick_stop.isra.1>
4b0: e3a00000 mov r0, #0
4b4: e8bd8010 pop {r4, pc}

Also, for me size of exynos_mct.o decreased from 84588 bytes
to 83956.

Signed-off-by: Alexey Klimov <[e-mail]>
Signed-off-by: Daniel Lezcano <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>

drivers/clocksource/exynos_mct.c

···
 static int exynos4_tick_set_next_event(unsigned long cycles,
 				       struct clock_event_device *evt)
 {
-	struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
+	struct mct_clock_event_device *mevt;
 
+	mevt = container_of(evt, struct mct_clock_event_device, evt);
 	exynos4_mct_tick_start(cycles, mevt);
-
 	return 0;
 }
 
 static int set_state_shutdown(struct clock_event_device *evt)
 {
-	exynos4_mct_tick_stop(this_cpu_ptr(&percpu_mct_tick));
+	struct mct_clock_event_device *mevt;
+
+	mevt = container_of(evt, struct mct_clock_event_device, evt);
+	exynos4_mct_tick_stop(mevt);
 	return 0;
 }
 
 static int set_state_periodic(struct clock_event_device *evt)
 {
-	struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
+	struct mct_clock_event_device *mevt;
 	unsigned long cycles_per_jiffy;
 
+	mevt = container_of(evt, struct mct_clock_event_device, evt);
 	cycles_per_jiffy = (((unsigned long long)NSEC_PER_SEC / HZ * evt->mult)
 			    >> evt->shift);
 	exynos4_mct_tick_stop(mevt);