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The PCI specs say that peer-to-peer DMA should be supported between any two devices that have a common upstream PCI-to-PCI bridge. But devices under different Root Ports don't share a common upstream bridge, and PCIe r4.0, sec 1.3.1, says routing peer-to-peer transactions between Root Ports in the same Root Complex is optional. Many Root Complexes, including AMD ZEN, *do* support peer-to-peer DMA even between Root Ports. Add a whitelist and allow peer-to-peer DMA if both participants are attached to a Root Complex known to support it. Link: https://lore.kernel.org/linux-pci/20190418115859.2394-1-christian.koenig@amd.com Signed-off-by: Christian König <christian.koenig@amd.com> [bhelgaas: changelog] Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Logan Gunthorpe <logang@deltatee.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.