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When a PCI device is suspended, it is normally the PCI core's job to save Config Space and put the device into a low power state. However drivers are allowed to assume these responsibilities. When they do, the PCI core can tell by looking at the state_saved flag in struct pci_dev: The flag is cleared before commencing the suspend sequence and it is set when pci_save_state() is called. If the PCI core finds the flag set late in the suspend sequence, it refrains from calling pci_save_state() itself. But there are two corner cases where the PCI core neglects to clear the flag before commencing the suspend sequence: * If a driver has legacy PCI PM callbacks, pci_legacy_suspend() neglects to clear the flag. The (stale) flag is subsequently queried by pci_legacy_suspend() itself and pci_legacy_suspend_late(). * If a device has no driver or its driver has no PCI PM callbacks, pci_pm_freeze() neglects to clear the flag. The (stale) flag is subsequently queried by pci_pm_freeze_noirq(). The flag may be set prior to suspend if the device went through error recovery: Drivers commonly invoke pci_restore_state() + pci_save_state() to restore Config Space after reset. The flag may also be set if drivers call pci_save_state() on probe to allow for recovery from subsequent errors. The result is that pci_legacy_suspend_late() and pci_pm_freeze_noirq() don't call pci_save_state() and so the state that will be restored on resume is the one recorded on last error recovery or on probe, not the one that the device had on suspend. If the two states happen to be identical, there's no problem. Reinstate clearing the flag in pci_legacy_suspend() and pci_pm_freeze(). The two functions used to do that until commit |
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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.