drm/tegra: Add back arm_iommu_detach_device()

DMA buffers of 2D/3D engines aren't mapped properly when
CONFIG_ARM_DMA_USE_IOMMU=y. The memory management code of Tegra DRM driver
has a longstanding overhaul overdue and it's not obvious where the problem
is in this case. Hence let's add back the old workaround which we already
had sometime before. It explicitly detaches DRM devices from the offending
implicit IOMMU domain. This fixes a completely broken 2d/3d drivers in
case of ARM32 multiplatform kernel config.

Cc: stable@vger.kernel.org
Fixes: fa6661b7 ("drm/tegra: Optionally attach clients to the IOMMU")
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/drm.c

@@ -22,6 +22,10 @@
 #include <drm/drm_prime.h>
 #include <drm/drm_vblank.h>
 
+#if IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)
+#include <asm/dma-iommu.h>
+#endif
+
 #include "dc.h"
 #include "drm.h"
 #include "gem.h"
@@ -945,6 +949,17 @@ int host1x_client_iommu_attach(struct host1x_client *client)
 	struct iommu_group *group = NULL;
 	int err;
 
+#if IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)
+	if (client->dev->archdata.mapping) {
+		struct dma_iommu_mapping *mapping =
+				to_dma_iommu_mapping(client->dev);
+		arm_iommu_detach_device(client->dev);
+		arm_iommu_release_mapping(mapping);
+
+		domain = iommu_get_domain_for_dev(client->dev);
+	}
+#endif
+
 	/*
 	 * If the host1x client is already attached to an IOMMU domain that is
 	 * not the shared IOMMU domain, don't try to attach it to a different