[PATCH 4.9 100/172] drm/etnaviv: trick drm_mm into giving out a low IOVA

Greg Kroah-Hartman
2017-07-03T13:44:03Z

From: Lucas Stach <l.stach@pengutronix.de>

[ 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@pengutronix.de>
Reviewed-by: Wladimir van der Laan <laanwj@gmail.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/etnaviv/etnaviv_mmu.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- 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(struc
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;