drm/i915/lrc: Clarify the format of the context image

Not only the context image consist of two parts (the PPHWSP, and the
logical context state), but we also allocate a header at the start of
for sharing data with GuC. Thus every lrc looks like this:

  | [guc]          | [hwsp] [logical state] |
  |<- our header ->|<- context image      ->|

So far, we have oversimplified whenever we use each of these parts of the
context, just because the GuC header happens to be in page 0, and the
(PP)HWSP is in page 1. But this had led to using the same define for more
than one meaning (as a page index in the lrc and as 1 page).

This patch adds defines for the GuC shared page, the PPHWSP page and the
start of the logical state. It also updated the places where the old
define was being used. Since we are not changing the size (or format) of
the context, there are no functional changes.

v2: Use PPHWSP index for hws again.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: intel-gvt-dev@lists.freedesktop.org
Link: http://patchwork.freedesktop.org/patch/msgid/20170712193032.27080-1-michel.thierry@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170913085605.18299-1-chris@chris-wilson.co.uk

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

@@ -87,7 +87,7 @@ static int populate_shadow_context(struct intel_vgpu_workload *workload)
 			return -EINVAL;
 		}
 
-		page = i915_gem_object_get_page(ctx_obj, LRC_PPHWSP_PN + i);
+		page = i915_gem_object_get_page(ctx_obj, LRC_HEADER_PAGES + i);
 		dst = kmap(page);
 		intel_gvt_hypervisor_read_gpa(vgpu, context_gpa, dst,
 				GTT_PAGE_SIZE);
@@ -454,7 +454,7 @@ static void update_guest_context(struct intel_vgpu_workload *workload)
 			return;
 		}
 
-		page = i915_gem_object_get_page(ctx_obj, LRC_PPHWSP_PN + i);
+		page = i915_gem_object_get_page(ctx_obj, LRC_HEADER_PAGES + i);
 		src = kmap(page);
 		intel_gvt_hypervisor_write_gpa(vgpu, context_gpa, src,
 				GTT_PAGE_SIZE);

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -1314,7 +1314,7 @@ int intel_guc_suspend(struct drm_i915_private *dev_priv)
 	/* any value greater than GUC_POWER_D0 */
 	data[1] = GUC_POWER_D1;
 	/* first page is shared data with GuC */
-	data[2] = guc_ggtt_offset(ctx->engine[RCS].state);
+	data[2] = guc_ggtt_offset(ctx->engine[RCS].state) + LRC_GUCSHR_PN * PAGE_SIZE;
 
 	return intel_guc_send(guc, data, ARRAY_SIZE(data));
 }
@@ -1340,7 +1340,7 @@ int intel_guc_resume(struct drm_i915_private *dev_priv)
 	data[0] = INTEL_GUC_ACTION_EXIT_S_STATE;
 	data[1] = GUC_POWER_D0;
 	/* first page is shared data with GuC */
-	data[2] = guc_ggtt_offset(ctx->engine[RCS].state);
+	data[2] = guc_ggtt_offset(ctx->engine[RCS].state) + LRC_GUCSHR_PN * PAGE_SIZE;
 
 	return intel_guc_send(guc, data, ARRAY_SIZE(data));
 }

drivers/gpu/drm/i915/intel_lrc.c

@@ -279,7 +279,7 @@ intel_lr_context_descriptor_update(struct i915_gem_context *ctx,
 	BUILD_BUG_ON(MAX_CONTEXT_HW_ID > (1<<GEN8_CTX_ID_WIDTH));
 
 	desc = ctx->desc_template;				/* bits  0-11 */
-	desc |= i915_ggtt_offset(ce->state) + LRC_PPHWSP_PN * PAGE_SIZE;
+	desc |= i915_ggtt_offset(ce->state) + LRC_HEADER_PAGES * PAGE_SIZE;
 								/* bits 12-31 */
 	desc |= (u64)ctx->hw_id << GEN8_CTX_ID_SHIFT;		/* bits 32-52 */
 
@@ -2048,8 +2048,11 @@ static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
 
 	context_size = round_up(engine->context_size, I915_GTT_PAGE_SIZE);
 
-	/* One extra page as the sharing data between driver and GuC */
-	context_size += PAGE_SIZE * LRC_PPHWSP_PN;
+	/*
+	 * Before the actual start of the context image, we insert a few pages
+	 * for our own use and for sharing with the GuC.
+	 */
+	context_size += LRC_HEADER_PAGES * PAGE_SIZE;
 
 	ctx_obj = i915_gem_object_create(ctx->i915, context_size);
 	if (IS_ERR(ctx_obj)) {

drivers/gpu/drm/i915/intel_lrc.h

@@ -70,10 +70,29 @@ int logical_xcs_ring_init(struct intel_engine_cs *engine);
 
 /* Logical Ring Contexts */
 
-/* One extra page is added before LRC for GuC as shared data */
+/*
+ * We allocate a header at the start of the context image for our own
+ * use, therefore the actual location of the logical state is offset
+ * from the start of the VMA. The layout is
+ *
+ * | [guc]          | [hwsp] [logical state] |
+ * |<- our header ->|<- context image      ->|
+ *
+ */
+/* The first page is used for sharing data with the GuC */
 #define LRC_GUCSHR_PN	(0)
-#define LRC_PPHWSP_PN	(LRC_GUCSHR_PN + 1)
-#define LRC_STATE_PN	(LRC_PPHWSP_PN + 1)
+#define LRC_GUCSHR_SZ	(1)
+/* At the start of the context image is its per-process HWS page */
+#define LRC_PPHWSP_PN	(LRC_GUCSHR_PN + LRC_GUCSHR_SZ)
+#define LRC_PPHWSP_SZ	(1)
+/* Finally we have the logical state for the context */
+#define LRC_STATE_PN	(LRC_PPHWSP_PN + LRC_PPHWSP_SZ)
+
+/*
+ * Currently we include the PPHWSP in __intel_engine_context_size() so
+ * the size of the header is synonymous with the start of the PPHWSP.
+ */
+#define LRC_HEADER_PAGES LRC_PPHWSP_PN
 
 struct drm_i915_private;
 struct i915_gem_context;