[Intel-gfx] [PATCH 03/16] drm/i915: return ctx->global_id from intel_execlists_ctx_id()

[sourab.gupta at intel.com]

From: Robert Bragg <robert at sixbynine.org>

The newly added intel_context::global_id is suitable (a globally unique
20 bit ID) for giving to the hardware as a unique context identifier.

Compared to using the pinned address of a logical ring context these IDs
are constant for the lifetime of a context whereas a context could be
repinned at different addresses during its lifetime.

Having a stable ID is useful when we need to buffer information
associated with a context based on this ID so the association can't be
lost. For example the OA unit writes out counter reports to a circular
buffer tagged with this ID and we want to be able to accurately filter
reports for a specific context, ideally without the added complexity of
tracking context re-pinning while the OA buffer may contain reports with
older IDs.

Cc: Sourab Gupta <sourab.gupta at intel.com>
Signed-off-by: Robert Bragg <robert at sixbynine.org>
---
 drivers/gpu/drm/i915/i915_debugfs.c |  4 ++--
 drivers/gpu/drm/i915/intel_lrc.c    | 28 ++++++++++++++--------------
 drivers/gpu/drm/i915/intel_lrc.h    |  3 +--
 3 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 931dc60..c172bf5 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2050,7 +2050,7 @@ static void i915_dump_lrc_obj(struct seq_file *m,
 	}
 
 	seq_printf(m, "CONTEXT: %s %u\n", engine->name,
-		   intel_execlists_ctx_id(ctx, engine));
+		   intel_execlists_ctx_id(ctx));
 
 	if (!i915_gem_obj_ggtt_bound(ctx_obj))
 		seq_puts(m, "\tNot bound in GGTT\n");
@@ -2171,7 +2171,7 @@ static int i915_execlists(struct seq_file *m, void *data)
 		seq_printf(m, "\t%d requests in queue\n", count);
 		if (head_req) {
 			seq_printf(m, "\tHead request id: %u\n",
-				   intel_execlists_ctx_id(head_req->ctx, engine));
+				   intel_execlists_ctx_id(head_req->ctx));
 			seq_printf(m, "\tHead request tail: %u\n",
 				   head_req->tail);
 		}
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 452ea0d..1425ede 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -307,21 +307,23 @@ logical_ring_init_platform_invariants(struct intel_engine_cs *engine)
  * This is what a descriptor looks like, from LSB to MSB:
  *    bits 0-11:    flags, GEN8_CTX_* (cached in ctx_desc_template)
  *    bits 12-31:    LRCA, GTT address of (the HWSP of) this context
- *    bits 32-51:    ctx ID, a globally unique tag (the LRCA again!)
+ *    bits 32-51:    ctx ID, a globally unique tag (ctx->global_id)
  *    bits 52-63:    reserved, may encode the engine ID (for GuC)
  */
 static void
 intel_lr_context_descriptor_update(struct intel_context *ctx,
 				   struct intel_engine_cs *engine)
 {
-	uint64_t lrca, desc;
+	uint64_t lrca, id, desc;
 
 	lrca = ctx->engine[engine->id].lrc_vma->node.start +
 	       LRC_PPHWSP_PN * PAGE_SIZE;
 
-	desc = engine->ctx_desc_template;			   /* bits  0-11 */
-	desc |= lrca;					   /* bits 12-31 */
-	desc |= (lrca >> PAGE_SHIFT) << GEN8_CTX_ID_SHIFT; /* bits 32-51 */
+	id = ctx->global_id;
+
+	desc = engine->ctx_desc_template;   /* bits  0-11 */
+	desc |= lrca;			    /* bits 12-31 */
+	desc |= id << GEN8_CTX_ID_SHIFT;    /* bits 32-51 */
 
 	ctx->engine[engine->id].lrc_desc = desc;
 }
@@ -335,7 +337,6 @@ uint64_t intel_lr_context_descriptor(struct intel_context *ctx,
 /**
  * intel_execlists_ctx_id() - get the Execlists Context ID
  * @ctx: Context to get the ID for
- * @ring: Engine to get the ID for
  *
  * Do not confuse with ctx->id! Unfortunately we have a name overload
  * here: the old context ID we pass to userspace as a handler so that
@@ -343,15 +344,14 @@ uint64_t intel_lr_context_descriptor(struct intel_context *ctx,
  * ELSP so that the GPU can inform us of the context status via
  * interrupts.
  *
- * The context ID is a portion of the context descriptor, so we can
- * just extract the required part from the cached descriptor.
- *
- * Return: 20-bits globally unique context ID.
+ * Further the ID given to HW can now be relied on to be constant for
+ * the lifetime of the context, unlike previously when we used an
+ * associated logical ring context address (which could be repinned at
+ * a different address).
  */
-u32 intel_execlists_ctx_id(struct intel_context *ctx,
-			   struct intel_engine_cs *engine)
+u32 intel_execlists_ctx_id(struct intel_context *ctx)
 {
-	return intel_lr_context_descriptor(ctx, engine) >> GEN8_CTX_ID_SHIFT;
+	return ctx->global_id;
 }
 
 static void execlists_elsp_write(struct drm_i915_gem_request *rq0,
@@ -501,7 +501,7 @@ execlists_check_remove_request(struct intel_engine_cs *engine, u32 request_id)
 	if (!head_req)
 		return 0;
 
-	if (unlikely(intel_execlists_ctx_id(head_req->ctx, engine) != request_id))
+	if (unlikely(intel_execlists_ctx_id(head_req->ctx) != request_id))
 		return 0;
 
 	WARN(head_req->elsp_submitted == 0, "Never submitted head request\n");
diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
index 461f1ef..a1ff58b 100644
--- a/drivers/gpu/drm/i915/intel_lrc.h
+++ b/drivers/gpu/drm/i915/intel_lrc.h
@@ -114,8 +114,7 @@ void intel_lr_context_reset(struct drm_i915_private *dev_priv,
 uint64_t intel_lr_context_descriptor(struct intel_context *ctx,
 				     struct intel_engine_cs *engine);
 
-u32 intel_execlists_ctx_id(struct intel_context *ctx,
-			   struct intel_engine_cs *engine);
+u32 intel_execlists_ctx_id(struct intel_context *ctx);
 
 /* Execlists */
 int intel_sanitize_enable_execlists(struct drm_device *dev, int enable_execlists);
-- 
1.9.1