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The test BAR is on the EP side is allocated using pci_epf_alloc_space(), which allocates the backing memory using dma_alloc_coherent(), which will return zeroed memory regardless of __GFP_ZERO was set or not. This means that running a new version of pci-endpoint-test.c (host side) with an old version of pci-epf-test.c (EP side) will not see any capabilities being set (as intended), so this is backwards compatible. Additionally, the EP side always allocates at least 128 bytes for the test BAR (excluding the MSI-X table), this means that adding another register at offset 0x30 is still within the 128 available bytes. For now, we only add the CAP_UNALIGNED_ACCESS capability. If CAP_UNALIGNED_ACCESS is set, that means that the EP side supports reading/writing to an address without any alignment requirements. Thus, if CAP_UNALIGNED_ACCESS is set, make sure that the host side does not add any extra padding to the buffers that we allocate (which was only done in order to get the buffers to satisfy certain alignment requirements by the endpoint controller). Link: https://lore.kernel.org/r/20241203063851.695733-6-cassel@kernel.org Signed-off-by: Niklas Cassel <cassel@kernel.org> Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> Reviewed-by: Frank Li <Frank.Li@nxp.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 reStructuredText 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.