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Linux kernel stable tree
d591f6804e
After a device reset, delays are required before the device can successfully complete config accesses. PCIe r6.0, sec 6.6, specifies some delays required before software can perform config accesses. Devices that require more time after those delays may respond to config accesses with Configuration Request Retry Status (RRS) completions. Callers of pci_dev_wait() are responsible for delays until the device can respond to config accesses. pci_dev_wait() waits any additional time until the device can successfully complete config accesses. Reading config space of devices that are not present or not ready typically returns ~0 (PCI_ERROR_RESPONSE). Previously we polled the Command register until we got a value other than ~0. This is sometimes a problem because Root Complex handling of RRS completions may include several retries and implementation-specific behavior that is invisible to software (see sec 2.3.2), so the exponential backoff in pci_dev_wait() may not work as intended. Linux enables Configuration RRS Software Visibility on all Root Ports that support it. If it is enabled, read the Vendor ID instead of the Command register. RRS completions cause immediate return of the 0x0001 reserved Vendor ID value, so the pci_dev_wait() backoff works correctly. When a read of Vendor ID eventually completes successfully by returning a non-0x0001 value (the Vendor ID or 0xffff for VFs), the device should be initialized and ready to respond to config requests. For conventional PCI devices or devices below Root Ports that don't support Configuration RRS Software Visibility, poll the Command register as before. This was developed independently, but is very similar to Stanislav Spassov's previous work at https://lore.kernel.org/linux-pci/20200223122057.6504-1-stanspas@amazon.com Link: https://lore.kernel.org/r/20240827234848.4429-2-helgaas@kernel.org Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Tested-by: Duc Dang <ducdang@google.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.