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In accordance with the generic PCIe Root Port DT-bindings the "dma-ranges" property has the same format as the "ranges" property. The only difference is in their semantics. The "dma-ranges" property describes the PCIe-to-CPU memory mapping in opposite to the CPU-to-PCIe mapping of the "ranges" property. Even though the DW PCIe controllers are normally equipped with the internal Address Translation Unit which inbound and outbound tables can be used to implement both properties semantics, it was surprising for me to discover that the host-related part of the DW PCIe driver currently supports the "ranges" property only while the "dma-ranges" windows are just ignored. Having the "dma-ranges" supported in the driver would be very handy for the platforms, that don't tolerate the 1:1 CPU-PCIe memory mapping and require a customized PCIe memory layout. So let's fix that by introducing the "dma-ranges" property support. First of all we suggest to rename the dw_pcie_prog_inbound_atu() method to dw_pcie_prog_ep_inbound_atu() and create a new version of the dw_pcie_prog_inbound_atu() function. Thus we'll have two methods for the RC and EP controllers respectively in the same way as it has been developed for the outbound ATU setup methods. Secondly aside with the memory window index and type the new dw_pcie_prog_inbound_atu() function will accept CPU address, PCIe address and size as its arguments. These parameters define the PCIe and CPU memory ranges which will be used to setup the respective inbound ATU mapping. The passed parameters need to be verified against the ATU ranges constraints in the same way as it is done for the outbound ranges. Finally the DMA-ranges detected for the PCIe controller need to be converted to the inbound ATU entries during the host controller initialization procedure. It will be done in the framework of the dw_pcie_iatu_setup() method. Note before setting the inbound ranges up we need to disable all the inbound ATU entries in order to prevent unexpected PCIe TLPs translations defined by some third party software like bootloaders. Link: https://lore.kernel.org/r/20221113191301.5526-16-Sergey.Semin@baikalelectronics.ru Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org> Reviewed-by: Rob Herring <robh@kernel.org> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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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.