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780d4223f6
The DU DMA address space is limited to 32 bits, so the DMA coherent mask should be set accordingly. The DMA mapping implementation will transparently map high memory buffers to 32-bit addresses through an IOMMU when present (or through bounce buffers otherwise, which isn't a supported use case as performances would be terrible). However, when sourcing frames from a VSP, the situation is more complicated. The DU delegates all memory accesses to the VSP and doesn't perform any DMA access by itself. Due to how the GEM CMA helpers are structured buffers are still mapped to the DU device. They are later mapped to the VSP as well to perform DMA access, through the IOMMU connected to the VSP. Setting the DMA coherent mask to 32 bits for the DU when using a VSP can cause issues when importing a dma_buf. If the buffer is located above the 32-bit address space, the DMA mapping implementation will try to map it to the DU's DMA address space. As the DU has no IOMMU a bounce buffer will be allocated, which in the best case will waste memory and in the worst case will just fail. To work around this issue, set the DMA coherent mask to the full 40-bit address space for the DU. All dma-buf instances will be imported without any restriction, and will be mapped to the VSP when preparing the associated framebuffer. Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> Reviewed-by: Liviu Dudau <liviu.dudau@arm.com> |
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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.