drm/i915/pmu: Deprecate I915_PMU_LAST and optimize state tracking

Adding any kinds of "last" abi markers is usually a mistake which I
repeated when implementing the PMU because it felt convenient at the time.

This patch marks I915_PMU_LAST as deprecated and stops the internal
implementation using it for sizing the event status bitmask and array.

New way of sizing the fields is a bit less elegant, but it omits reserving
slots for tracking events we are not interested in, and as such saves some
runtime space. Adding sampling events is likely to be a special event and
the new plumbing needed will be easily detected in testing. Existing
asserts against the bitfield and array sizes are keeping the code safe.

First event which gets the new treatment in this new scheme are the
interrupts - which neither needs any tracking in i915 pmu nor needs
waking up the GPU to read it.

v2:
 * Streamline helper names. (Chris)

v3:
 * Comment which events need tracking. (Chris)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20201201131757.206367-1-tvrtko.ursulin@linux.intel.com

1 files changed, 24 insertions, 11 deletions

diff --git a/drivers/gpu/drm/i915/i915_pmu.h b/drivers/gpu/drm/i915/i915_pmu.h
index a24885ab415c..e33be99e6454 100644
--- a/drivers/gpu/drm/i915/i915_pmu.h
+++ b/drivers/gpu/drm/i915/i915_pmu.h
@@ -14,6 +14,21 @@
 
 struct drm_i915_private;
 
+/**
+ * Non-engine events that we need to track enabled-disabled transition and
+ * current state.
+ */
+enum i915_pmu_tracked_events {
+	__I915_PMU_ACTUAL_FREQUENCY_ENABLED = 0,
+	__I915_PMU_REQUESTED_FREQUENCY_ENABLED,
+	__I915_PMU_RC6_RESIDENCY_ENABLED,
+	__I915_PMU_TRACKED_EVENT_COUNT, /* count marker */
+};
+
+/**
+ * Slots used from the sampling timer (non-engine events) with some extras for
+ * convenience.
+ */
 enum {
 	__I915_SAMPLE_FREQ_ACT = 0,
 	__I915_SAMPLE_FREQ_REQ,
@@ -28,8 +43,7 @@ enum {
  * It is also used to know to needed number of event reference counters.
  */
 #define I915_PMU_MASK_BITS \
-	((1 << I915_PMU_SAMPLE_BITS) + \
-	 (I915_PMU_LAST + 1 - __I915_PMU_OTHER(0)))
+	(I915_ENGINE_SAMPLE_COUNT + __I915_PMU_TRACKED_EVENT_COUNT)
 
 #define I915_ENGINE_SAMPLE_COUNT (I915_SAMPLE_SEMA + 1)
 
@@ -66,18 +80,17 @@ struct i915_pmu {
 	 */
 	struct hrtimer timer;
 	/**
-	 * @enable: Bitmask of all currently enabled events.
+	 * @enable: Bitmask of specific enabled events.
+	 *
+	 * For some events we need to track their state and do some internal
+	 * house keeping.
 	 *
-	 * Bits are derived from uAPI event numbers in a way that low 16 bits
-	 * correspond to engine event _sample_ _type_ (I915_SAMPLE_QUEUED is
-	 * bit 0), and higher bits correspond to other events (for instance
-	 * I915_PMU_ACTUAL_FREQUENCY is bit 16 etc).
+	 * Each engine event sampler type and event listed in enum
+	 * i915_pmu_tracked_events gets a bit in this field.
 	 *
-	 * In other words, low 16 bits are not per engine but per engine
-	 * sampler type, while the upper bits are directly mapped to other
-	 * event types.
+	 * Low bits are engine samplers and other events continue from there.
 	 */
-	u64 enable;
+	u32 enable;
 
 	/**
 	 * @timer_last: