drm/nouveau/instmem/gk20a: set DMA mask early

DMA mask is typically set in nouveau_ttm_init(), but this function is
called late during initialization and GK20A's instmem will have called
DMA functions before this happens.

Having a wrongly set DMA mask can result in the use of unneeded bounce
buffers. Set it early to avoid this.
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c

@@ -280,6 +280,15 @@ nvkm_device_tegra_new(const struct nvkm_device_tegra_func *func,
 		goto free;
 	}
 
+	/**
+	 * The IOMMU bit defines the upper limit of the GPU-addressable space.
+	 * This will be refined in nouveau_ttm_init but we need to do it early
+	 * for instmem to behave properly
+	 */
+	ret = dma_set_mask(&pdev->dev, DMA_BIT_MASK(tdev->func->iommu_bit));
+	if (ret)
+		goto free;
+
 	nvkm_device_tegra_probe_iommu(tdev);
 
 	ret = nvkm_device_tegra_power_up(tdev);