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077092783a
On R-Car Gen3, the DU uses a separate IP core named VSP to perform DMA from memory and composition of planes. The DU hardware then only handles the video timings and the interface with the encoders. This differs from Gen2, where the DU included a composer with DMA engines. When sourcing from the VSP, the DU hardware performs no memory access, and thus has no requirements on imported dma-buf memory types. The GEM CMA helpers however still create a DMA mapping to the DU device, which isn't used. The mapping to the VSP is done when processing the atomic commits, in the plane .prepare_fb() handler. When the system uses an IOMMU, the VSP device is attached to it, which enables the VSP to use non physically contiguous memory. The DU, as it performs no memory access, isn't connected to the IOMMU. The GEM CMA drm_gem_cma_prime_import_sg_table() helper will in that case fail to map non-contiguous imported dma-bufs, as the DMA mapping to the DU device will have multiple entries in its sgtable. The prevents using non physically contiguous memory for display. The DRM PRIME and GEM CMA helpers are designed to create the sgtable when the dma-buf is imported. By default, the device referenced by the drm_device is used to create the dma-buf attachment. Drivers can use a different device by using the drm_gem_prime_import_dev() function. While the DU has access to the VSP device, this won't help here, as different CRTCs use different VSP instances, connected to different IOMMU channels. The driver doesn't know at import time which CRTC a GEM object will be used, and thus can't select the right VSP device to pass to drm_gem_prime_import_dev(). To support non-contiguous memory, implement a custom .gem_prime_import_sg_table() operation that accepts all imported dma-buf regardless of the number of scatterlist entries. The sgtable will be mapped to the VSP at .prepare_fb() time, which will reject the framebuffer if the VSP isn't connected to an IOMMU. Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.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.