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The StarFive JH7100 SoC has non-coherent device DMAs, but most drivers expect to be able to allocate coherent memory for DMA descriptors and such. However on the JH7100 DDR memory appears twice in the physical memory map, once cached and once uncached: 0x00_8000_0000 - 0x08_7fff_ffff : Off chip DDR memory, cached 0x10_0000_0000 - 0x17_ffff_ffff : Off chip DDR memory, uncached To use this uncached region we create a global DMA memory pool there and reserve the corresponding area in the cached region. However the uncached region is fully above the 32bit address limit, so add a dma-ranges map so the DMA address used for peripherals is still in the regular cached region below the limit. Link: https://github.com/starfive-tech/JH7100_Docs/blob/main/JH7100%20Data%20Sheet%20V01.01.04-EN%20(4-21-2021).pdf Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com> Signed-off-by: Conor Dooley <conor.dooley@microchip.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.