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The PCIe bandwidth controller added by a subsequent commit will require selecting PCIe Link Speeds that are lower than the Maximum Link Speed. The struct pci_bus only stores max_bus_speed. Even if PCIe r6.1 sec 8.2.1 currently disallows gaps in supported Link Speeds, the Implementation Note in PCIe r6.1 sec 7.5.3.18, recommends determining supported Link Speeds using the Supported Link Speeds Vector in the Link Capabilities 2 Register (when available) to "avoid software being confused if a future specification defines Links that do not require support for all slower speeds." Reuse code in pcie_get_speed_cap() to add pcie_get_supported_speeds() to query the Supported Link Speeds Vector of a PCIe device. The value is taken directly from the Supported Link Speeds Vector or synthesized from the Max Link Speed in the Link Capabilities Register when the Link Capabilities 2 Register is not available. The Supported Link Speeds Vector in the Link Capabilities Register 2 corresponds to the bus below on Root Ports and Downstream Ports, whereas it corresponds to the bus above on Upstream Ports and Endpoints (PCIe r6.1 sec 7.5.3.18): Supported Link Speeds Vector - This field indicates the supported Link speed(s) of the associated Port. Add supported_speeds into the struct pci_dev that caches the Supported Link Speeds Vector. supported_speeds contains a set of Link Speeds only in the case where PCIe Link Speed can be determined. Root Complex Integrated Endpoints do not have a well-defined Link Speed because they do not implement either of the Link Capabilities Registers, which is allowed by PCIe r6.1 sec 7.5.3 (the same limitation applies to determining cur_bus_speed and max_bus_speed that are PCI_SPEED_UNKNOWN in such case). This is of no concern from PCIe bandwidth controller point of view because such devices are not attached into a PCIe Root Port that could be controlled. The supported_speeds field keeps the extra reserved zero at the least significant bit to match the Link Capabilities 2 Register layout. An attempt was made to store supported_speeds field into the struct pci_bus as an intersection of both ends of the Link, however, the subordinate struct pci_bus is not available early enough. The Target Speed quirk (in pcie_failed_link_retrain()) can run either during initial scan or later, requiring it to use the API provided by the PCIe bandwidth controller to set the Target Link Speed in order to co-exist with the bandwidth controller. When the Target Speed quirk is calling the bandwidth controller during initial scan, the struct pci_bus is not yet initialized. As such, storing supported_speeds into the struct pci_bus is not viable. Suggested-by: Lukas Wunner <lukas@wunner.de> Link: https://lore.kernel.org/r/20241018144755.7875-4-ilpo.jarvinen@linux.intel.com Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> [bhelgaas: move pcie_get_supported_speeds() decl to drivers/pci/pci.h] Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> |
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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.