drm/xe/lrc: Add helper to capture context timestamp

Add a helper to capture CTX_TIMESTAMP from the context image so it can
be used to calculate the runtime.

v2: Add kernel-doc to clarify expectation from caller
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517204310.88854-4-lucas.demarchi@intel.comSigned-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

drivers/gpu/drm/xe/regs/xe_lrc_layout.h

@@ -11,6 +11,7 @@
 #define CTX_RING_TAIL			(0x06 + 1)
 #define CTX_RING_START			(0x08 + 1)
 #define CTX_RING_CTL			(0x0a + 1)
+#define CTX_TIMESTAMP			(0x22 + 1)
 #define CTX_INDIRECT_RING_STATE		(0x26 + 1)
 #define CTX_PDP0_UDW			(0x30 + 1)
 #define CTX_PDP0_LDW			(0x32 + 1)

drivers/gpu/drm/xe/xe_lrc.c

@@ -844,6 +844,7 @@ int xe_lrc_init(struct xe_lrc *lrc, struct xe_hw_engine *hwe,
 	lrc->tile = gt_to_tile(hwe->gt);
 	lrc->ring.size = ring_size;
 	lrc->ring.tail = 0;
+	lrc->ctx_timestamp = 0;
 
 	xe_hw_fence_ctx_init(&lrc->fence_ctx, hwe->gt,
 			     hwe->fence_irq, hwe->name);
@@ -898,6 +899,8 @@ int xe_lrc_init(struct xe_lrc *lrc, struct xe_hw_engine *hwe,
 				     RING_CTL_SIZE(lrc->ring.size) | RING_VALID);
 	}
 
+	xe_lrc_write_ctx_reg(lrc, CTX_TIMESTAMP, 0);
+
 	if (xe->info.has_asid && vm)
 		xe_lrc_write_ctx_reg(lrc, PVC_CTX_ASID, vm->usm.asid);
 
@@ -1576,3 +1579,12 @@ void xe_lrc_snapshot_free(struct xe_lrc_snapshot *snapshot)
 		xe_bo_put(snapshot->lrc_bo);
 	kfree(snapshot);
 }
+
+u32 xe_lrc_update_timestamp(struct xe_lrc *lrc, u32 *old_ts)
+{
+	*old_ts = lrc->ctx_timestamp;
+
+	lrc->ctx_timestamp = xe_lrc_read_ctx_reg(lrc, CTX_TIMESTAMP);
+
+	return lrc->ctx_timestamp;
+}

drivers/gpu/drm/xe/xe_lrc.h

@@ -66,4 +66,18 @@ void xe_lrc_snapshot_capture_delayed(struct xe_lrc_snapshot *snapshot);
 void xe_lrc_snapshot_print(struct xe_lrc_snapshot *snapshot, struct drm_printer *p);
 void xe_lrc_snapshot_free(struct xe_lrc_snapshot *snapshot);
 
+/**
+ * xe_lrc_update_timestamp - readout LRC timestamp and update cached value
+ * @lrc: logical ring context for this exec queue
+ * @old_ts: pointer where to save the previous timestamp
+ *
+ * Read the current timestamp for this LRC and update the cached value. The
+ * previous cached value is also returned in @old_ts so the caller can calculate
+ * the delta between 2 updates. Note that this is not intended to be called from
+ * any place, but just by the paths updating the drm client utilization.
+ *
+ * Returns the current LRC timestamp
+ */
+u32 xe_lrc_update_timestamp(struct xe_lrc *lrc, u32 *old_ts);
+
 #endif

drivers/gpu/drm/xe/xe_lrc_types.h

@@ -45,6 +45,9 @@ struct xe_lrc {
 
 	/** @fence_ctx: context for hw fence */
 	struct xe_hw_fence_ctx fence_ctx;
+
+	/** @ctx_timestamp: readout value of CTX_TIMESTAMP on last update */
+	u32 ctx_timestamp;
 };
 
 struct xe_lrc_snapshot;