drm/i915/perf: Apply Wa_18013179988

OA reports in the OA buffer contain an OA timestamp field that helps
user calculate delta between 2 OA reports. The calculation relies on the
CS timestamp frequency to convert the timestamp value to nanoseconds.
The CS timestamp frequency is a function of the CTC_SHIFT value in
RPM_CONFIG0.

In DG2, OA unit assumes that the CTC_SHIFT is 3, instead of using the
actual value from RPM_CONFIG0. At the user level, this results in an
error in calculating delta between 2 OA reports since the OA timestamp
is not shifted in the same manner as CS timestamp. Also the periodicity
of the reports is different from what the user configured because of
mismatch in the CS and OA frequencies.

The issue also affects MI_REPORT_PERF_COUNT command.

To resolve this, return actual OA timestamp frequency to the user in
i915_getparam_ioctl, so that user can calculate the right OA exponent as
well as interpret the reports correctly.

MR: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18893

v2:
- Use REG_FIELD_GET (Ashutosh)
- Update commit msg
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221026222102.5526-13-umesh.nerlige.ramappa@intel.com

drivers/gpu/drm/i915/i915_getparam.c

@@ -175,6 +175,9 @@ int i915_getparam_ioctl(struct drm_device *dev, void *data,
 	case I915_PARAM_PERF_REVISION:
 		value = i915_perf_ioctl_version();
 		break;
+	case I915_PARAM_OA_TIMESTAMP_FREQUENCY:
+		value = i915_perf_oa_timestamp_frequency(i915);
+		break;
 	default:
 		DRM_DEBUG("Unknown parameter %d\n", param->param);
 		return -EINVAL;

drivers/gpu/drm/i915/i915_perf.c

@@ -3109,6 +3109,30 @@ get_sseu_config(struct intel_sseu *out_sseu,
 	return i915_gem_user_to_context_sseu(engine->gt, drm_sseu, out_sseu);
 }
 
+/*
+ * OA timestamp frequency = CS timestamp frequency in most platforms. On some
+ * platforms OA unit ignores the CTC_SHIFT and the 2 timestamps differ. In such
+ * cases, return the adjusted CS timestamp frequency to the user.
+ */
+u32 i915_perf_oa_timestamp_frequency(struct drm_i915_private *i915)
+{
+	/* Wa_18013179988:dg2 */
+	if (IS_DG2(i915)) {
+		intel_wakeref_t wakeref;
+		u32 reg, shift;
+
+		with_intel_runtime_pm(to_gt(i915)->uncore->rpm, wakeref)
+			reg = intel_uncore_read(to_gt(i915)->uncore, RPM_CONFIG0);
+
+		shift = REG_FIELD_GET(GEN10_RPM_CONFIG0_CTC_SHIFT_PARAMETER_MASK,
+				      reg);
+
+		return to_gt(i915)->clock_frequency << (3 - shift);
+	}
+
+	return to_gt(i915)->clock_frequency;
+}
+
 /**
  * i915_oa_stream_init - validate combined props for OA stream and init
  * @stream: An i915 perf stream
@@ -3830,8 +3854,10 @@ i915_perf_open_ioctl_locked(struct i915_perf *perf,
 
 static u64 oa_exponent_to_ns(struct i915_perf *perf, int exponent)
 {
-	return intel_gt_clock_interval_to_ns(to_gt(perf->i915),
-					     2ULL << exponent);
+	u64 nom = (2ULL << exponent) * NSEC_PER_SEC;
+	u32 den = i915_perf_oa_timestamp_frequency(perf->i915);
+
+	return div_u64(nom + den - 1, den);
 }
 
 static __always_inline bool

drivers/gpu/drm/i915/i915_perf.h

@@ -57,4 +57,6 @@ static inline void i915_oa_config_put(struct i915_oa_config *oa_config)
 	kref_put(&oa_config->ref, i915_oa_config_release);
 }
 
+u32 i915_perf_oa_timestamp_frequency(struct drm_i915_private *i915);
+
 #endif /* __I915_PERF_H__ */

include/uapi/drm/i915_drm.h

@@ -765,6 +765,12 @@ typedef struct drm_i915_irq_wait {
 /* Query if the kernel supports the I915_USERPTR_PROBE flag. */
 #define I915_PARAM_HAS_USERPTR_PROBE 56
 
+/*
+ * Frequency of the timestamps in OA reports. This used to be the same as the CS
+ * timestamp frequency, but differs on some platforms.
+ */
+#define I915_PARAM_OA_TIMESTAMP_FREQUENCY 57
+
 /* Must be kept compact -- no holes and well documented */
 
 /**