drm/etnaviv: space out IOVA layout for cmdbufs on MMUv2

At least on the GC3000 the FE MMU is not properly flushing stale TLB
entries. Make sure to map the cmdbufs with a big enough spacing in
the IOVAs to not hit old/prefetched TLB entries when jumping to a
newly mapped cmdbuf.

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

drivers/gpu/drm/etnaviv/etnaviv_mmu.c

@@ -342,7 +342,12 @@ u32 etnaviv_iommu_get_cmdbuf_va(struct etnaviv_gpu *gpu,
 			mutex_unlock(&mmu->lock);
 			return 0;
 		}
-		mmu->last_iova = buf->vram_node.start + buf->size;
+		/*
+		 * At least on GC3000 the FE MMU doesn't properly flush old TLB
+		 * entries. Make sure to space the command buffers out in a way
+		 * that the FE MMU prefetch won't load invalid entries.
+		 */
+		mmu->last_iova = buf->vram_node.start + buf->size + SZ_64K;
 		gpu->mmu->need_flush = true;
 		mutex_unlock(&mmu->lock);