drm/etnaviv: keep MMU context across runtime suspend/resume

The MMU state may be kept across a runtime suspend/resume cycle, as we
avoid a full hardware reset to keep the latency of the runtime PM small.

Don't pretend that the MMU state is lost in driver state. The MMU
context is pushed out when new HW jobs with a different context are
coming in. The only exception to this is when the GPU is unbound, in
which case we need to make sure to also free the last active context.

Cc: stable@vger.kernel.org # 5.4
Reported-by: NMichael Walle <michael@walle.cc>
Signed-off-by: NLucas Stach <l.stach@pengutronix.de>
Tested-by: NMichael Walle <michael@walle.cc>
Tested-by: NMarek Vasut <marex@denx.de>
Reviewed-by: NChristian Gmeiner <christian.gmeiner@gmail.com>

drivers/gpu/drm/etnaviv/etnaviv_gpu.c

@@ -1596,9 +1596,6 @@ static int etnaviv_gpu_hw_suspend(struct etnaviv_gpu *gpu)
 		 */
 		etnaviv_gpu_wait_idle(gpu, 100);
 
-		etnaviv_iommu_context_put(gpu->mmu_context);
-		gpu->mmu_context = NULL;
-
 		gpu->fe_running = false;
 	}
 
@@ -1747,6 +1744,9 @@ static void etnaviv_gpu_unbind(struct device *dev, struct device *master,
 	etnaviv_gpu_hw_suspend(gpu);
 #endif
 
+	if (gpu->mmu_context)
+		etnaviv_iommu_context_put(gpu->mmu_context);
+
 	if (gpu->initialized) {
 		etnaviv_cmdbuf_free(&gpu->buffer);
 		etnaviv_iommu_global_fini(gpu);