drm/i915: Let execlist_update_context() cover !FULL_PPGTT mode.

execlist_update_context() will try to update PDPs in a context before a
ELSP submission only for full PPGTT mode, while PDPs was populated during
context initialization. Now the latter code path is removed. Let
execlist_update_context() also cover !FULL_PPGTT mode.

Fixes: 34869776c76b ("drm/i915: check ppgtt validity when init reg state")
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhiyuan Lv <zhiyuan.lv@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1486377436-15380-1-git-send-email-zhi.a.wang@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_lrc.c

@@ -321,7 +321,8 @@ execlists_update_context_pdps(struct i915_hw_ppgtt *ppgtt, u32 *reg_state)
 static u64 execlists_update_context(struct drm_i915_gem_request *rq)
 {
 	struct intel_context *ce = &rq->ctx->engine[rq->engine->id];
-	struct i915_hw_ppgtt *ppgtt = rq->ctx->ppgtt;
+	struct i915_hw_ppgtt *ppgtt =
+		rq->ctx->ppgtt ?: rq->i915->mm.aliasing_ppgtt;
 	u32 *reg_state = ce->lrc_reg_state;
 
 	reg_state[CTX_RING_TAIL+1] = rq->tail;