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a2f1e22390
When the PCI core gained power management support in 2002, it introduced pci_save_state() and pci_restore_state() helpers to restore Config Space after a D3hot or D3cold transition, which implies a Soft or Fundamental Reset (PCIe r7.0 sec 5.8): https://git.kernel.org/tglx/history/c/a5287abe398b In 2006, EEH and AER were introduced to recover from errors by performing a reset. Because errors can occur at any time, drivers began calling pci_save_state() on probe to ensure recoverability. In 2009, recoverability was foiled by commitc82f63e411("PCI: check saved state before restore"): It amended pci_restore_state() to bail out if the "state_saved" flag has been cleared. The flag is cleared by pci_restore_state() itself, hence a saved state is now allowed to be restored only once and is then invalidated. That doesn't seem to make sense because the saved state should be good enough to be reused. Soon after, drivers began to work around this behavior by calling pci_save_state() immediately after pci_restore_state(), see e.g. commitb94f2d775a("igb: call pci_save_state after pci_restore_state"). Hilariously, two drivers even set the "saved_state" flag to true before invoking pci_restore_state(), see ipr_reset_restore_cfg_space() and e1000_io_slot_reset(). Despite these workarounds, recoverability at all times is not guaranteed: E.g. when a PCIe port goes through a runtime suspend and resume cycle, the "saved_state" flag is cleared by: pci_pm_runtime_resume() pci_pm_default_resume_early() pci_restore_state() ... and hence on a subsequent AER event, the port's Config Space cannot be restored. Riana reports a recovery failure of a GPU-integrated PCIe switch and has root-caused it to the behavior of pci_restore_state(). Another workaround would be necessary, namely calling pci_save_state() in pcie_port_device_runtime_resume(). The motivation of commitc82f63e411was to prevent restoring state if pci_save_state() hasn't been called before. But that can be achieved by saving state already on device addition, after Config Space has been initialized. A desirable side effect is that devices become recoverable even if no driver gets bound. This renders the commit unnecessary, so revert it. Reported-by: Riana Tauro <riana.tauro@intel.com> # off-list Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Tested-by: Riana Tauro <riana.tauro@intel.com> Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org> Link: https://patch.msgid.link/9e34ce61c5404e99ffdd29205122c6fb334b38aa.1763483367.git.lukas@wunner.de
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.