Re: [PATCH 1/2] drm/tegra: Set DMA ops

[Alexandre Courbot]

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:
> > 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 <acourbot@xxxxxxxxxx>
> > ---
> >   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.