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After recovering from a PCI error through reset, affected devices are in D0_uninitialized state and need to be brought into D0_active state by re-initializing their Config Space registers (PCIe r7.0 sec 5.3.1.1). To facilitate that, the PCI core provides pci_restore_state() and pci_save_state() helpers. Document rules governing their usage. As Bjorn notes, so far no file in "Documentation/ includes anything about the idea of a driver using pci_save_state() to capture the state it wants to restore after an error", even though it is a common pattern in drivers. So that's obviously a gap that should be closed. Reported-by: Bjorn Helgaas <helgaas@kernel.org> Closes: https://lore.kernel.org/r/20251113161556.GA2284238@bhelgaas/ Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org> Link: https://patch.msgid.link/077596ba70202be0e43fdad3bb9b93d356cbe4ec.1763746079.git.lukas@wunner.de