drm/etnaviv: block 64K of address space behind each cmdstream

To make sure we don't place anything there which might confuse
the FE prefetcher. This gets rid of another case of FE MMU faults
when the address space gets crowded before triggering the reaper.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_mmu.c

@@ -330,7 +330,8 @@ u32 etnaviv_iommu_get_cmdbuf_va(struct etnaviv_gpu *gpu,
 			return (u32)buf->vram_node.start;
 
 		mutex_lock(&mmu->lock);
-		ret = etnaviv_iommu_find_iova(mmu, &buf->vram_node, buf->size);
+		ret = etnaviv_iommu_find_iova(mmu, &buf->vram_node,
+					      buf->size + SZ_64K);
 		if (ret < 0) {
 			mutex_unlock(&mmu->lock);
 			return 0;