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The MSI target address must be in the lowest 4GB memory to support PCI peripherals without 64-bit MSI support. Since the allocation is done from DMA coherent memory, set only the coherent DMA mask, leaving the streaming DMA mask alone. Thus streaming DMA operations will work with no artificial limitations. It will be specifically useful for the eDMA-capable controllers so the corresponding DMA engine clients would map the DMA buffers with no need for SWIOTLB for buffers allocated above 4GB. Add a brief comment about the reason allocating the MSI target address below 4GB. Link: https://lore.kernel.org/r/20230113171409.30470-26-Sergey.Semin@baikalelectronics.ru Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Robin Murphy <robin.murphy@arm.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.