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If the Tegra DRM clients are backed by an IOMMU, push buffers are likely to be allocated beyond the 32-bit boundary if sufficient system memory is available. This is problematic on earlier generations of Tegra where host1x supports a maximum of 32 address bits for the GATHER opcode. More recent versions of Tegra (Tegra186 and later) have a wide variant of the GATHER opcode, which allows addressing up to 64 bits of memory. If host1x itself is behind an IOMMU as well this doesn't matter because the IOMMU's input address space is restricted to 32 bits on generations without support for wide GATHER opcodes. However, if host1x is not behind an IOMMU, it won't be able to process push buffers beyond the 32-bit boundary on Tegra generations that don't support wide GATHER opcodes. Restrict the DMA mask to 32 bits on these generations prevents buffers from being allocated from beyond the 32-bit boundary. Signed-off-by: Thierry Reding <treding@nvidia.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.