Revert "drm/i915: Kill GTT mappings when moving from GTT domain"

This reverts commit 4a684a4117abd756291969336af454e8a958802f.
Userland has always been required to set the object's domain to GTT
before using it through a GTT mapping, it's not something that the
kernel is supposed to enforce.  (The pagefault support is so that we
can handle multiple mappings without userland having to pin across
them, not so that userland can use GTT after GPU domains without
telling the kernel).

Fixes 19.2% +/- 0.8% (n=6) performance regression in cairo-gl
firefox-talos-gfx on my T420 latop.

Signed-off-by: Keith Packard <keithp@keithp.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 94c84d7..c6389de 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1219,11 +1219,11 @@
 		ret = i915_gem_object_bind_to_gtt(obj, 0, true);
 		if (ret)
 			goto unlock;
-	}
 
-	ret = i915_gem_object_set_to_gtt_domain(obj, write);
-	if (ret)
-		goto unlock;
+		ret = i915_gem_object_set_to_gtt_domain(obj, write);
+		if (ret)
+			goto unlock;
+	}
 
 	if (obj->tiling_mode == I915_TILING_NONE)
 		ret = i915_gem_object_put_fence(obj);
@@ -2926,8 +2926,6 @@
 	 */
 	wmb();
 
-	i915_gem_release_mmap(obj);
-
 	old_write_domain = obj->base.write_domain;
 	obj->base.write_domain = 0;
 
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 20a4cc5..4934cf8 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -187,10 +187,6 @@
 	if ((flush_domains | invalidate_domains) & I915_GEM_DOMAIN_CPU)
 		i915_gem_clflush_object(obj);
 
-	/* blow away mappings if mapped through GTT */
-	if ((flush_domains | invalidate_domains) & I915_GEM_DOMAIN_GTT)
-		i915_gem_release_mmap(obj);
-
 	if (obj->base.pending_write_domain)
 		cd->flips |= atomic_read(&obj->pending_flip);