[PATCH] drm/i915: A hotfix for making aliasing PPGTT work

[Zhi Wang <zhi.a.wang@intel.com>]

This patch makes PPGTT page table non-shrinkable when using aliasing PPGTT
mode. It's just a temporary solution for making aliasing PPGTT mode work.

v2:
- Add fixes tag. (Chris and Daniel)

Fixes commit 2ce5179fe826 ("drm/i915/gtt: Free unused lower-level page tables")
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
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: Daniel Vetter <daniel.vetter@intel.com>
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/1486559013-25251-2-git-send-email-zhi.a.wang@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.10-rc1+
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 22b3374..3233f12 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -756,8 +756,10 @@ static bool gen8_ppgtt_clear_pt(struct i915_address_space *vm,
 
 	bitmap_clear(pt->used_ptes, pte, num_entries);
 
-	if (bitmap_empty(pt->used_ptes, GEN8_PTES))
-		return true;
+	if (USES_FULL_PPGTT(vm->i915)) {
+		if (bitmap_empty(pt->used_ptes, GEN8_PTES))
+			return true;
+	}
 
 	pt_vaddr = kmap_px(pt);
 
-- 
1.9.1

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