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Some IDT switches incorrectly flag an ACS Source Validation error on completions for config read requests even though PCIe r4.0, sec 6.12.1.1, says that completions are never affected by ACS Source Validation. Here's the text of IDT 89H32H8G3-YC, erratum #36: Item #36 - Downstream port applies ACS Source Validation to Completions Section 6.12.1.1 of the PCI Express Base Specification 3.1 states that completions are never affected by ACS Source Validation. However, completions received by a downstream port of the PCIe switch from a device that has not yet captured a PCIe bus number are incorrectly dropped by ACS Source Validation by the switch downstream port. Workaround: Issue a CfgWr1 to the downstream device before issuing the first CfgRd1 to the device. This allows the downstream device to capture its bus number; ACS Source Validation no longer stops completions from being forwarded by the downstream port. It has been observed that Microsoft Windows implements this workaround already; however, some versions of Linux and other operating systems may not. When doing the first config read to probe for a device, if the device is behind an IDT switch with this erratum: 1. Disable ACS Source Validation if enabled 2. Wait for device to become ready to accept config accesses (by using the Config Request Retry Status mechanism) 3. Do a config write to the endpoint 4. Enable ACS Source Validation (if it was enabled to begin with) The workaround suggested by IDT is basically only step 3, but we don't know when the device is ready to accept config requests. That means we need to do config reads until we receive a non-Config Request Retry Status, which means we need to disable ACS SV temporarily. Signed-off-by: James Puthukattukaran <james.puthukattukaran@oracle.com> [bhelgaas: changelog, clean up whitespace, fold in unused variable fix from Anders Roxell <anders.roxell@linaro.org>] Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Alex Williamson <alex.williamson@redhat.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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.