[PATCH 2/2] drm/tegra: Set the DMA mask
tbergstrom at nvidia.com
Tue Feb 23 16:18:26 UTC 2016
On 02/23/2016 08:04 AM, Thierry Reding wrote:
> * PGP Signed by an unknown key > > On Tue, Feb 23, 2016 at 03:25:54PM +0900, Alexandre Courbot wrote:
>> The default DMA mask covers a 32 bits address range, but tegradrm >>
can address more than that. Set the DMA mask to the actual >>
addressable range to avoid the use of unneeded bounce buffers. >> >>
Signed-off-by: Alexandre Courbot <acourbot at nvidia.com> --- Thierry, >> I
am not absolutely sure whether the size is correct and applies to >> all
Tegra generations - please let me know if this needs to be >> reworked.
>> >> drivers/gpu/drm/tegra/drm.c | 1 + 1 file changed, 1 insertion(+)
> > This kind of depends on whether or not the device is behind an
IOMMU. > If it is, then the IOMMU DMA MASK would apply, which can be
derived > from the number of address bits that the IOMMU can handle. The
SMMU > supports 32 address bits on Tegra30 and Tegra114, 34 address bits
on > more recent generations. > > I think for now it's safer to leave
the DMA mask at the default (32 > bit) to avoid the need to distinguish
between IOMMU and non-IOMMU > devices.
The GPUs after Tegra114 can choose per access whether they're using IOMMU
or not. The interface is 34 bits wide, so the physical addresses can be
IOMMU addresses are limited by Tegra SMMU to 32-bit for gk20a. gm20b can use
34-bit if SMMU is configured to combine four ASIDs together.
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