drm/i915/bdw: A bit more advanced LR context alloc/free

Now that we have the ability to allocate our own context backing objects
and we have multiplexed one of them per engine inside the context structs,
we can finally allocate and free them correctly.

Regarding the context size, reading the register to calculate the sizes
can work, I think, however the docs are very clear about the actual
context sizes on GEN8, so just hardcode that and use it.

v2: Rebased on top of the Full PPGTT series. It is important to notice
that at this point we have one global default context per engine, all
of them using the aliasing PPGTT (as opposed to the single global
default context we have with legacy HW contexts).

v3:
- Go back to one single global default context, this time with multiple
  backing objects inside.
- Use different context sizes for non-render engines, as suggested by
  Damien (still hardcoded, since the information about the context size
  registers in the BSpec is, well, *lacking*).
- Render ctx size is 20 (or 19) pages, but not 21 (caught by Damien).
- Move default context backing object creation to intel_init_ring (so
  that we don't waste memory in rings that might not get initialized).

v4:
- Reuse the HW legacy context init/fini.
- Create a separate free function.
- Rename the functions with an intel_ preffix.

v5: Several rebases to account for the changes in the previous patches.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v1)
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -2528,6 +2528,8 @@ int i915_switch_context(struct intel_engine_cs *ring,
 struct intel_context *
 i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id);
 void i915_gem_context_free(struct kref *ctx_ref);
+struct drm_i915_gem_object *
+i915_gem_alloc_context_obj(struct drm_device *dev, size_t size);
 static inline void i915_gem_context_reference(struct intel_context *ctx)
 {
 	kref_get(&ctx->ref);

drivers/gpu/drm/i915/i915_gem_context.c

@@ -199,7 +199,7 @@ void i915_gem_context_free(struct kref *ctx_ref)
 	kfree(ctx);
 }
 
-static struct drm_i915_gem_object *
+struct drm_i915_gem_object *
 i915_gem_alloc_context_obj(struct drm_device *dev, size_t size)
 {
 	struct drm_i915_gem_object *obj;

drivers/gpu/drm/i915/intel_lrc.c

@@ -41,6 +41,11 @@
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
 
+#define GEN8_LR_CONTEXT_RENDER_SIZE (20 * PAGE_SIZE)
+#define GEN8_LR_CONTEXT_OTHER_SIZE (2 * PAGE_SIZE)
+
+#define GEN8_LR_CONTEXT_ALIGN 4096
+
 int intel_sanitize_enable_execlists(struct drm_device *dev, int enable_execlists)
 {
 	WARN_ON(i915.enable_ppgtt == -1);
@@ -56,15 +61,65 @@ int intel_sanitize_enable_execlists(struct drm_device *dev, int enable_execlists
 
 void intel_lr_context_free(struct intel_context *ctx)
 {
-	/* TODO */
+	int i;
+
+	for (i = 0; i < I915_NUM_RINGS; i++) {
+		struct drm_i915_gem_object *ctx_obj = ctx->engine[i].state;
+		if (ctx_obj) {
+			i915_gem_object_ggtt_unpin(ctx_obj);
+			drm_gem_object_unreference(&ctx_obj->base);
+		}
+	}
+}
+
+static uint32_t get_lr_context_size(struct intel_engine_cs *ring)
+{
+	int ret = 0;
+
+	WARN_ON(INTEL_INFO(ring->dev)->gen != 8);
+
+	switch (ring->id) {
+	case RCS:
+		ret = GEN8_LR_CONTEXT_RENDER_SIZE;
+		break;
+	case VCS:
+	case BCS:
+	case VECS:
+	case VCS2:
+		ret = GEN8_LR_CONTEXT_OTHER_SIZE;
+		break;
+	}
+
+	return ret;
 }
 
 int intel_lr_context_deferred_create(struct intel_context *ctx,
 				     struct intel_engine_cs *ring)
 {
+	struct drm_device *dev = ring->dev;
+	struct drm_i915_gem_object *ctx_obj;
+	uint32_t context_size;
+	int ret;
+
 	WARN_ON(ctx->legacy_hw_ctx.rcs_state != NULL);
 
-	/* TODO */
+	context_size = round_up(get_lr_context_size(ring), 4096);
+
+	ctx_obj = i915_gem_alloc_context_obj(dev, context_size);
+	if (IS_ERR(ctx_obj)) {
+		ret = PTR_ERR(ctx_obj);
+		DRM_DEBUG_DRIVER("Alloc LRC backing obj failed: %d\n", ret);
+		return ret;
+	}
+
+	ret = i915_gem_obj_ggtt_pin(ctx_obj, GEN8_LR_CONTEXT_ALIGN, 0);
+	if (ret) {
+		DRM_DEBUG_DRIVER("Pin LRC backing obj failed: %d\n", ret);
+		drm_gem_object_unreference(&ctx_obj->base);
+		return ret;
+	}
+
+	ctx->engine[ring->id].state = ctx_obj;
 
 	return 0;
 }