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77e9c198b1
The scripts/dtc/checks.c requires that the node have empty "dma-ranges" property must have the same "#address-cells" and "#size-cells" values as the parent node. Otherwise, the following warnings is reported: arch/arm64/boot/dts/qcom/ipq6018.dtsi:185.3-14: Warning \ (dma_ranges_format): /soc:dma-ranges: empty "dma-ranges" property but \ its #address-cells (1) differs from / (2) arch/arm64/boot/dts/qcom/ipq6018.dtsi:185.3-14: Warning \ (dma_ranges_format): /soc:dma-ranges: empty "dma-ranges" property but \ its #size-cells (1) differs from / (2) Arnd Bergmann figured out why it's necessary: Also note that the #address-cells=<1> means that any device under this bus is assumed to only support 32-bit addressing, and DMA will have to go through a slow swiotlb in the absence of an IOMMU. Suggested-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> Link: https://lore.kernel.org/r/20201016090833.1892-3-thunder.leizhen@huawei.com Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
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.