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After commit4fb8e46c1b("PCI: tegra194: Enable support for 256 Byte payload"), we initialize MPS=256 for tegra194 Root Ports before enumerating the hierarchy. Consider an Endpoint that supports only MPS=128. In the default situation (CONFIG_PCIE_BUS_DEFAULT set and no "pci=pcie_bus_*" parameter), Linux tries to configure the MPS of every device to match the upstream bridge. If the Endpoint is directly below the Root Port, Linux can reduce the Root Port MPS to 128 to match the Endpoint. But if there's a switch in the middle, Linux doesn't reduce the Root Port MPS because other devices below the switch may already be configured with MPS larger than 128. This scenario results in uncorrectable Malformed TLP errors if the Root Port sends TLPs with payloads larger than 128 bytes. These errors can be avoided by using the "pci=pcie_bus_safe" parameter, but it doesn't seem to be a good idea to always have this parameter even for basic functionality to work. Revert commit4fb8e46c1b("PCI: tegra194: Enable support for 256 Byte payload") so the Root Ports default to MPS=128, which all devices support. If peer-to-peer DMA is not required, one can use "pci=pcie_bus_perf" to get the benefit of larger MPS settings. [bhelgaas: commit log; kwilczynski: retain "u16 val_16" declaration at the top, add missing acked by tag] Fixes:4fb8e46c1b("PCI: tegra194: Enable support for 256 Byte payload") Link: https://lore.kernel.org/linux-pci/20230619102604.3735001-1-vidyas@nvidia.com Signed-off-by: Vidya Sagar <vidyas@nvidia.com> Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org> Acked-by: Jon Hunter <jonathanh@nvidia.com> Cc: stable@vger.kernel.org # v6.0-rc1+
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.