intel-gpu-overlay: Use RAPL PMU for power reading

Wire up to the RAPL PMU for GPU energy readings.

The only complication is that we have to add code to parse:

 # cat /sys/devices/power/events/energy-gpu.scale
 2.3283064365386962890625e-10

v2: Link with -lm.
v3: strtod can handle scientific notation, even though my initial
    reading of the man page did not spot that. (Chris Wilson)
v4: Meson fix.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/overlay/power.h b/overlay/power.h
index bf8346ce..28abfc32 100644
--- a/overlay/power.h
+++ b/overlay/power.h
@@ -39,6 +39,8 @@ struct power {
 	int new_sample;
 
 	uint64_t power_mW;
+
+	double rapl_scale;
 };
 
 int power_init(struct power *power);