On 02/24/2016 12:28 AM, Thierry Reding wrote:

* PGP Signed by an unknown key

On Tue, Feb 23, 2016 at 03:25:53PM +0900, Alexandre Courbot wrote:

quoted

The current settings leaves the DRM device's dma_ops field NULL, which
makes it use the dummy DMA ops on arm64 and return an error whenever we
try to import a buffer. Call of_dma_configure() with a NULL node (since
the device is not spawn from the device tree) so that
arch_setup_dma_ops() is called and sets the default ioswtlb DMA ops.

Signed-off-by: Alexandre Courbot <redacted>
---
  drivers/gpu/drm/tegra/drm.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index d347188bf8f4..bc0555adecaf 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c

@@ -9,6 +9,7 @@

  #include <linux/host1x.h>
  #include <linux/iommu.h>
+#include <linux/of_device.h>

  #include <drm/drm_atomic.h>
  #include <drm/drm_atomic_helper.h>

@@ -990,6 +991,7 @@ static int host1x_drm_probe(struct host1x_device *dev)
  		return -ENOMEM;

  	dev_set_drvdata(&dev->dev, drm);
+	of_dma_configure(drm->dev, NULL);

Looking at the various pieces, I think this really belongs in
host1x_device_add() (see drivers/gpu/host1x/bus.c) where it can replace
the open-coded setting of DMA and coherent DMA masks. Also why can't we
pass the correct device tree node here? The DRM device is a virtual
device that hangs off the host1x device, so I think it could use the
same device tree node as the host1x device.

Something like the below (untested).

You're right, that looks like a much better place to do this. 
of_dma_configure() is called at the bus level (platform and PCI), so it 
makes sense to do it from host1x too.