Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH 12/18] iommu/tegra-gart: Add IOMMU_DOMAIN_DMA support | From | Dmitry Osipenko <> | Date | Thu, 20 Aug 2020 23:16:02 +0300 |
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20.08.2020 18:08, Robin Murphy пишет: > Now that arch/arm is wired up for default domains and iommu-dma, > implement the corresponding driver-side support for DMA domains. > > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > drivers/iommu/tegra-gart.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c > index fac720273889..e081387080f6 100644 > --- a/drivers/iommu/tegra-gart.c > +++ b/drivers/iommu/tegra-gart.c > @@ -9,6 +9,7 @@ > > #define dev_fmt(fmt) "gart: " fmt > > +#include <linux/dma-iommu.h> > #include <linux/io.h> > #include <linux/iommu.h> > #include <linux/moduleparam.h> > @@ -145,16 +146,22 @@ static struct iommu_domain *gart_iommu_domain_alloc(unsigned type) > { > struct iommu_domain *domain;
Hello, Robin!
Tegra20 GART isn't a real IOMMU, but a small relocation aperture. We would only want to use it for a temporal mappings (managed by GPU driver) for the time while GPU hardware is busy and working with a sparse DMA buffers, the driver will take care of unmapping the sparse buffers once GPU work is finished [1]. In a case of contiguous DMA buffers, we want to bypass the IOMMU and use buffer's phys address because GART aperture is small and all buffers simply can't fit into GART for a complex GPU operations that involve multiple buffers [2][3]. The upstream GPU driver still doesn't support GART, but eventually it needs to be changed.
[1] https://github.com/grate-driver/linux/blob/master/drivers/gpu/drm/tegra/gart.c#L489
[2] https://github.com/grate-driver/linux/blob/master/drivers/gpu/drm/tegra/gart.c#L542
[3] https://github.com/grate-driver/linux/blob/master/drivers/gpu/drm/tegra/uapi/patching.c#L90
> - if (type != IOMMU_DOMAIN_UNMANAGED) > + if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA) > return NULL;
Will a returned NULL tell to IOMMU core that implicit domain shouldn't be used? Is it possible to leave this driver as-is?
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