[PATCH] drm/etnaviv: trick drm_mm into giving out a low IOVA

[Lucas Stach]

After rollover of the IOVA space, we want to get a low IOVA address,
otherwise the the games we play by remembering the last IOVA are
pointless. When we search for a free hole with DRM_MM_SEARCH_DEFAULT,
drm_mm will pop the next entry from the free holes stack, which will
likely be a high IOVA. By using DRM_MM_SEARCH_BELOW we can trick
drm_mm into reversing the search and provide us with a low IOVA.

Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
This is intended to fix the GPU MMU fault on a <= 4.10 kernel. Later
kernels will hopefully fix this by removing the IOVA gaming completely,
but this will need some bigger re-writes of the code in question.
---
 drivers/gpu/drm/etnaviv/etnaviv_mmu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
index 169ac96e8f08..fe0e85b41310 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
@@ -116,9 +116,14 @@ static int etnaviv_iommu_find_iova(struct etnaviv_iommu *mmu,
 		struct list_head list;
 		bool found;
 
+		/*
+		 * XXX: The DRM_MM_SEARCH_BELOW is really a hack to trick
+		 * drm_mm into giving out a low IOVA after address space
+		 * rollover. This needs a proper fix.
+		 */
 		ret = drm_mm_insert_node_in_range(&mmu->mm, node,
 			size, 0, mmu->last_iova, ~0UL,
-			DRM_MM_SEARCH_DEFAULT);
+			mmu->last_iova ? DRM_MM_SEARCH_DEFAULT : DRM_MM_SEARCH_BELOW);
 
 		if (ret != -ENOSPC)
 			break;
-- 
2.10.2