drm/i915/guc: Copy whole golden context, set engine state size of subset

When the GuC does a media reset, it copies a golden context state back
into the corrupted context's state. The address of the golden context
and the size of the engine state restore are passed in via the GuC ADS.
The i915 had a bug where it passed in the whole size of the golden
context, not the size of the engine state to restore resulting in a
memory corruption.

Also copy the entire golden context on init rather than just the engine
state that is restored.

v2 (Daniele): use defines to avoid duplicated const variables (John).

Fixes: 481d458c ("drm/i915/guc: Add golden context to GuC ADS")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210909164744.31249-11-matthew.brost@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c

@@ -349,6 +349,8 @@ static void fill_engine_enable_masks(struct intel_gt *gt,
 	info->engine_enabled_masks[GUC_VIDEOENHANCE_CLASS] = VEBOX_MASK(gt);
 }
 
+#define LR_HW_CONTEXT_SIZE (80 * sizeof(u32))
+#define LRC_SKIP_SIZE (LRC_PPHWSP_SZ * PAGE_SIZE + LR_HW_CONTEXT_SIZE)
 static int guc_prep_golden_context(struct intel_guc *guc,
 				   struct __guc_ads_blob *blob)
 {
@@ -396,7 +398,18 @@ static int guc_prep_golden_context(struct intel_guc *guc,
 		if (!blob)
 			continue;
 
-		blob->ads.eng_state_size[guc_class] = real_size;
+		/*
+		 * This interface is slightly confusing. We need to pass the
+		 * base address of the full golden context and the size of just
+		 * the engine state, which is the section of the context image
+		 * that starts after the execlists context. This is required to
+		 * allow the GuC to restore just the engine state when a
+		 * watchdog reset occurs.
+		 * We calculate the engine state size by removing the size of
+		 * what comes before it in the context image (which is identical
+		 * on all engines).
+		 */
+		blob->ads.eng_state_size[guc_class] = real_size - LRC_SKIP_SIZE;
 		blob->ads.golden_context_lrca[guc_class] = addr_ggtt;
 		addr_ggtt += alloc_size;
 	}
@@ -436,11 +449,6 @@ static void guc_init_golden_context(struct intel_guc *guc)
 	u8 engine_class, guc_class;
 	u8 *ptr;
 
-	/* Skip execlist and PPGTT registers + HWSP */
-	const u32 lr_hw_context_size = 80 * sizeof(u32);
-	const u32 skip_size = LRC_PPHWSP_SZ * PAGE_SIZE +
-		lr_hw_context_size;
-
 	if (!intel_uc_uses_guc_submission(&gt->uc))
 		return;
 
@@ -476,12 +484,12 @@ static void guc_init_golden_context(struct intel_guc *guc)
 			continue;
 		}
 
-		GEM_BUG_ON(blob->ads.eng_state_size[guc_class] != real_size);
+		GEM_BUG_ON(blob->ads.eng_state_size[guc_class] !=
+			   real_size - LRC_SKIP_SIZE);
 		GEM_BUG_ON(blob->ads.golden_context_lrca[guc_class] != addr_ggtt);
 		addr_ggtt += alloc_size;
 
-		shmem_read(engine->default_state, skip_size, ptr + skip_size,
-			   real_size - skip_size);
+		shmem_read(engine->default_state, 0, ptr, real_size);
 		ptr += alloc_size;
 	}