Revert "drm/i915/execlists: Reset RING registers upon resume"

This reverts commit f2a0409a which is
commit bafb2f7d upstream.

It was reported to have problems.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Eric Blau <eblau1@gmail.com>
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

drivers/gpu/drm/i915/intel_lrc.c

@@ -2152,42 +2152,30 @@ static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
 
 void intel_lr_context_resume(struct drm_i915_private *dev_priv)
 {
+	struct i915_gem_context *ctx = dev_priv->kernel_context;
 	struct intel_engine_cs *engine;
-	struct i915_gem_context *ctx;
-
-	/* Because we emit WA_TAIL_DWORDS there may be a disparity
-	 * between our bookkeeping in ce->ring->head and ce->ring->tail and
-	 * that stored in context. As we only write new commands from
-	 * ce->ring->tail onwards, everything before that is junk. If the GPU
-	 * starts reading from its RING_HEAD from the context, it may try to
-	 * execute that junk and die.
-	 *
-	 * So to avoid that we reset the context images upon resume. For
-	 * simplicity, we just zero everything out.
-	 */
-	list_for_each_entry(ctx, &dev_priv->context_list, link) {
+
 	for_each_engine(engine, dev_priv) {
 		struct intel_context *ce = &ctx->engine[engine->id];
-			u32 *reg;
+		void *vaddr;
+		uint32_t *reg_state;
 
 		if (!ce->state)
 			continue;
 
-			reg = i915_gem_object_pin_map(ce->state->obj,
-						      I915_MAP_WB);
-			if (WARN_ON(IS_ERR(reg)))
+		vaddr = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
+		if (WARN_ON(IS_ERR(vaddr)))
 			continue;
 
-			reg += LRC_STATE_PN * PAGE_SIZE / sizeof(*reg);
-			reg[CTX_RING_HEAD+1] = 0;
-			reg[CTX_RING_TAIL+1] = 0;
+		reg_state = vaddr + LRC_STATE_PN * PAGE_SIZE;
+
+		reg_state[CTX_RING_HEAD+1] = 0;
+		reg_state[CTX_RING_TAIL+1] = 0;
 
 		ce->state->obj->dirty = true;
 		i915_gem_object_unpin_map(ce->state->obj);
 
-			ce->ring->head = ce->ring->tail = 0;
-			ce->ring->last_retired_head = -1;
-			intel_ring_update_space(ce->ring);
-		}
+		ce->ring->head = 0;
+		ce->ring->tail = 0;
 	}
 }