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Currently, pci_bridge_d3_possible() encodes a variety of decision factors when deciding whether a given bridge can be put into D3. A particular one of note is for "recent enough PCIe ports." Per Rafael [0]: "There were hardware issues related to PM on x86 platforms predating the introduction of Connected Standby in Windows. For instance, programming a port into D3hot by writing to its PMCSR might cause the PCIe link behind it to go down and the only way to revive it was to power cycle the Root Complex. And similar." Thus, this function contains a DMI-based check for post-2015 BIOS. The above factors (Windows, x86) don't really apply to non-x86 systems, and also, many such systems don't have BIOS or DMI. However, we'd like to be able to suspend bridges on non-x86 systems too. Restrict the "recent enough" check to x86. If we find further incompatibilities, it probably makes sense to expand on the deny-list approach (i.e., bridge_d3_blacklist or similar). Link: https://lore.kernel.org/r/20250320110604.v6.1.Id0a0e78ab0421b6bce51c4b0b87e6aebdfc69ec7@changeid Link: https://lore.kernel.org/linux-pci/CAJZ5v0j_6jeMAQ7eFkZBe5Yi+USGzysxAgfemYh=-zq4h5W+Qg@mail.gmail.com/ [0] Link: https://lore.kernel.org/linux-pci/20240227225442.GA249898@bhelgaas/ [1] Link: https://lore.kernel.org/linux-pci/20240828210705.GA37859@bhelgaas/ [2] [Brian: rewrite to !X86 based on Rafael's suggestions] Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> Signed-off-by: Brian Norris <briannorris@chromium.org> Signed-off-by: Bjorn Helgaas <bhelgaas@google.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.