This automatically selects options for zone DMA and 64 bit DMA addresses
when LPAE is enabled on ARM Tegra platforms. These options are required
for proper operation with LPAE enabled.
The ZONE_DMA option is required to ensure that drivers that allocate DMA
memory get buffers from the first 4 GiB. This is necessary because a lot
of the controllers only support addressing 32 bits.
As for ARCH_DMA_ADDR_T_64BIT, there are situations where devices that do
support addresses of more than 32 bits (such as the display controller
or the GPU) can run without translating addresses through an IOMMU on a
device with more than 4 GiB of system memory.
Note that both of these options are stop-gap solutions required only
until the IOMMU can be properly integrated with the DMA mapping API and
drivers use that properly and consistently.
Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
[treding@nvidia.com: specify rationale for options]
Signed-off-by: Thierry Reding <treding@nvidia.com>
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