drm/i915/gvt: Do not allocate initial ring scan buffer

Theoretically, the largest bulk of commands in the ring buffer of an
engine might be the first submission, which usually contains a lot
of commands to initialize the HW. After removing the initial allocation
of the ring scan buffer and let krealloc() do everything we need, we
still have a big chance to get the buffer of suitable size in the first
submission.

Tested on my SKL NUC.
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>

drivers/gpu/drm/i915/gvt/execlist.c

@@ -872,36 +872,15 @@ void intel_vgpu_clean_execlist(struct intel_vgpu *vgpu)
 	}
 }
 
-#define RESERVE_RING_BUFFER_SIZE		((1 * PAGE_SIZE)/8)
 int intel_vgpu_init_execlist(struct intel_vgpu *vgpu)
 {
-	struct intel_vgpu_submission *s = &vgpu->submission;
 	enum intel_engine_id i;
 	struct intel_engine_cs *engine;
 
 	for_each_engine(engine, vgpu->gvt->dev_priv, i)
 		init_vgpu_execlist(vgpu, i);
 
-	/* each ring has a shadow ring buffer until vgpu destroyed */
-	for_each_engine(engine, vgpu->gvt->dev_priv, i) {
-		s->ring_scan_buffer[i] =
-			kmalloc(RESERVE_RING_BUFFER_SIZE, GFP_KERNEL);
-		if (!s->ring_scan_buffer[i]) {
-			gvt_vgpu_err("fail to alloc ring scan buffer\n");
-			goto out;
-		}
-		s->ring_scan_buffer_size[i] = RESERVE_RING_BUFFER_SIZE;
-	}
 	return 0;
-out:
-	for_each_engine(engine, vgpu->gvt->dev_priv, i) {
-		if (s->ring_scan_buffer_size[i]) {
-			kfree(s->ring_scan_buffer[i]);
-			s->ring_scan_buffer[i] = NULL;
-			s->ring_scan_buffer_size[i] = 0;
-		}
-	}
-	return -ENOMEM;
 }
 
 void intel_vgpu_reset_execlist(struct intel_vgpu *vgpu,

drivers/gpu/drm/i915/gvt/gvt.h

@@ -150,7 +150,6 @@ struct intel_vgpu_submission {
 	struct i915_gem_context *shadow_ctx;
 	DECLARE_BITMAP(shadow_ctx_desc_updated, I915_NUM_ENGINES);
 	DECLARE_BITMAP(tlb_handle_pending, I915_NUM_ENGINES);
-	/* 1/2K for each engine */
 	void *ring_scan_buffer[I915_NUM_ENGINES];
 	int ring_scan_buffer_size[I915_NUM_ENGINES];
 };