[PATCH for v4.9 LTS 51/86] drm/etnaviv: trick drm_mm into giving out a low IOVA

From: Levin, Alexander (Sasha Levin)
Date: Sat Jun 17 2017 - 18:36:08 EST

From: Lucas Stach <l.stach@xxxxxxxxxxxxxx>

[ Upstream commit 3546fb0cdac25a79c89d87020566fab52b92867d ]

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@xxxxxxxxxxxxxx>
Reviewed-by: Wladimir van der Laan <laanwj@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
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,

if (ret != -ENOSPC)