[RFC 34/60] drm/i915: introduce kernel blitter_context

[Matthew Auld <matthew.auld@xxxxxxxxx>]

We may be without a context to perform various internal blitter
operations, for example when performing object migration. Piggybacking
off the kernel_context is probably a bad idea, since it has other uses.

Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Abdiel Janulgue <abdiel.janulgue@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/gt/intel_engine_cs.c    | 30 +++++++++++++++++---
 drivers/gpu/drm/i915/gt/intel_engine_types.h |  1 +
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index dd1a42c4d344..1df94e82550f 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -792,6 +792,7 @@ create_kernel_context(struct intel_engine_cs *engine)
 	int err;
 
 	ce = intel_context_create(engine);
+
 	if (IS_ERR(ce))
 		return ce;
 
@@ -845,16 +846,32 @@ static int engine_init_common(struct intel_engine_cs *engine)
 		return PTR_ERR(ce);
 
 	ret = measure_breadcrumb_dw(ce);
-	if (ret < 0)
-		goto err_context;
+	if (ret < 0) {
+		intel_context_put(ce);
+		return ret;
+	}
 
 	engine->emit_fini_breadcrumb_dw = ret;
 	engine->kernel_context = ce;
 
+	/*
+	 * The blitter context is used to quickly memset or migrate objects
+	 * in local memory, so it has to always be available.
+	 */
+	if (engine->class == COPY_ENGINE_CLASS) {
+		ce = create_kernel_context(engine);
+		if (IS_ERR(ce)) {
+			ret = PTR_ERR(ce);
+			goto err_kernel_context;
+		}
+
+		engine->blitter_context = ce;
+	}
+
 	return 0;
 
-err_context:
-	intel_context_put(ce);
+err_kernel_context:
+	intel_context_put(engine->kernel_context);
 	return ret;
 }
 
@@ -910,6 +927,11 @@ void intel_engine_cleanup_common(struct intel_engine_cs *engine)
 	if (engine->default_state)
 		fput(engine->default_state);
 
+	if (engine->blitter_context) {
+		intel_context_unpin(engine->blitter_context);
+		intel_context_put(engine->blitter_context);
+	}
+
 	if (engine->kernel_context) {
 		intel_context_unpin(engine->kernel_context);
 		intel_context_put(engine->kernel_context);
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index 490af81bd6f3..3b2d9ed7670f 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -342,6 +342,7 @@ struct intel_engine_cs {
 	struct llist_head barrier_tasks;
 
 	struct intel_context *kernel_context; /* pinned */
+	struct intel_context *blitter_context; /* pinned; exists for BCS only */
 
 	intel_engine_mask_t saturated; /* submitting semaphores too late? */
 
-- 
2.26.2

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