[PATCH RFC 050/111] staging: etnaviv: hack: bypass iommu with contiguous buffers

[Lucas Stach]

From: Russell King <rmk+kernel at arm.linux.org.uk>

Bypass the iommu when we are dealing with single-entry scatterlists.

The etnaviv iommu code needs to be more inteligent: as it currently
stands, it is unusable as it always allocates from the bottom upwards.
This causes entries to be re-used without the MMU TLB being flushed,
but in order to flush the MMU TLB, we have to insert a command into
the GPU command stream.  Doing this for every allocation/free is
really sub-optimal.

To get things working as it currently stands, bypass this so that the
armada DRM scanout buffer can at least be used with etnaviv DRM.  This
at least gets us /some/ usable acceleration on Dove.

To fix this properly, the MMU handing needs to be re-evaluated and
probably rewritten.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 drivers/staging/etnaviv/etnaviv_mmu.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/etnaviv/etnaviv_mmu.c b/drivers/staging/etnaviv/etnaviv_mmu.c
index 2effe75cb154..4589995b83ff 100644
--- a/drivers/staging/etnaviv/etnaviv_mmu.c
+++ b/drivers/staging/etnaviv/etnaviv_mmu.c
@@ -99,6 +99,20 @@ int etnaviv_iommu_map_gem(struct etnaviv_iommu *mmu,
 	struct drm_mm_node *node = NULL;
 	int ret;
 
+	/* v1 MMU can optimize single entry (contiguous) scatterlists */
+	if (sgt->nents == 1) {
+		uint32_t iova;
+
+		iova = sg_dma_address(sgt->sgl);
+		if (!iova)
+			iova = sg_phys(sgt->sgl) - sgt->sgl->offset;
+
+		if (iova < 0x80000000 - sg_dma_len(sgt->sgl)) {
+			etnaviv_obj->iova = iova;
+			return 0;
+		}
+	}
+
 	node = kzalloc(sizeof(*node), GFP_KERNEL);
 	if (!node)
 		return -ENOMEM;
@@ -123,7 +137,7 @@ int etnaviv_iommu_map_gem(struct etnaviv_iommu *mmu,
 void etnaviv_iommu_unmap_gem(struct etnaviv_iommu *mmu,
 	struct etnaviv_gem_object *etnaviv_obj)
 {
-	if (etnaviv_obj->iova) {
+	if (etnaviv_obj->gpu_vram_node) {
 		uint32_t offset = etnaviv_obj->gpu_vram_node->start;
 
 		etnaviv_iommu_unmap(mmu, offset, etnaviv_obj->sgt,
-- 
2.1.4