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DMA engines used with displays perform 2D interleaved transfers to read framebuffers from memory and feed the data to the display engine. As the same framebuffer can be displayed for multiple frames, the DMA transactions need to be repeated until a new framebuffer replaces the current one. This feature is implemented natively by some DMA engines that have the ability to repeat transactions and switch to a new transaction at the end of a transfer without any race condition or frame loss. This patch implements support for this feature in the DMA engine API. A new DMA_PREP_REPEAT transaction flag allows DMA clients to instruct the DMA channel to repeat the transaction automatically until one or more new transactions are issued on the channel (or until all active DMA transfers are explicitly terminated with the dmaengine_terminate_*() functions). A new DMA_REPEAT transaction type is also added for DMA engine drivers to report their support of the DMA_PREP_REPEAT flag. A new DMA_PREP_LOAD_EOT transaction flag is also introduced (with a corresponding DMA_LOAD_EOT capability bit), as requested during the review of v4. The flag instructs the DMA channel that the transaction being queued should replace the active repeated transaction when the latter terminates (at End Of Transaction). Not setting the flag will result in the active repeated transaction to continue being repeated, and the new transaction being silently ignored. The DMA_PREP_REPEAT flag is currently supported for interleaved transactions only. Its usage can easily be extended to cover more transaction types simply by adding an appropriate check in the corresponding dmaengine_prep_*() function. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com> Link: https://lore.kernel.org/r/20200717013337.24122-3-laurent.pinchart@ideasonboard.com Signed-off-by: Vinod Koul <vkoul@kernel.org> |
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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.