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

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@pengutronix.de>
Reviewed-by: Wladimir van der Laan <laanwj@gmail.com>

1 files changed, 6 insertions, 1 deletions

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;