drm/i915/selftest: Fix ktime_get() and h/w access order

Use ktime_get() after accessing the mmio or any driver resource,
while using wall time for various calculation that depends on
the inserted delay in order to account any mmio and resource
access latency.

Cc: Chris Wilson <chris.p.wilson@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230223100503.3323627-3-anshuman.gupta@intel.com

drivers/gpu/drm/i915/gt/selftest_rps.c

@@ -537,8 +537,8 @@ static u64 __measure_frequency(u32 *cntr, int duration_ms)
 {
 	u64 dc, dt;
 
-	dt = ktime_get();
 	dc = READ_ONCE(*cntr);
+	dt = ktime_get();
 	usleep_range(1000 * duration_ms, 2000 * duration_ms);
 	dc = READ_ONCE(*cntr) - dc;
 	dt = ktime_get() - dt;
@@ -566,8 +566,8 @@ static u64 __measure_cs_frequency(struct intel_engine_cs *engine,
 {
 	u64 dc, dt;
 
-	dt = ktime_get();
 	dc = intel_uncore_read_fw(engine->uncore, CS_GPR(0));
+	dt = ktime_get();
 	usleep_range(1000 * duration_ms, 2000 * duration_ms);
 	dc = intel_uncore_read_fw(engine->uncore, CS_GPR(0)) - dc;
 	dt = ktime_get() - dt;
@@ -1094,8 +1094,8 @@ static u64 __measure_power(int duration_ms)
 {
 	u64 dE, dt;
 
-	dt = ktime_get();
 	dE = librapl_energy_uJ();
+	dt = ktime_get();
 	usleep_range(1000 * duration_ms, 2000 * duration_ms);
 	dE = librapl_energy_uJ() - dE;
 	dt = ktime_get() - dt;