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We leave PCI devices not bound to a driver in D0 during runtime suspend. But they may have a parent which is bound and can be transitioned to D3cold at runtime. Once the parent goes to D3cold, the unbound child may go to D3cold as well. When the child goes to D3cold, its internal state, including configuration of BARs, MSI, ASPM, MPS, etc., is lost. One example are recent hybrid graphics laptops which cut power to the discrete GPU when the root port above it goes to ACPI power state D3. Users may provoke this by unbinding the GPU driver and allowing runtime PM on the GPU via sysfs: The PM core will then treat the GPU as "suspended", which in turn allows the root port to runtime suspend, causing the power resources listed in its _PR3 object to be powered off. The GPU's BARs will be uninitialized when a driver later probes it. Another example are hybrid graphics laptops where the GPU itself (rather than the root port) is capable of runtime suspending to D3cold. If the GPU's integrated HDA controller is not bound and the GPU's driver decides to runtime suspend to D3cold, the HDA controller's BARs will be uninitialized when a driver later probes it. Fix by saving and restoring config space over a runtime suspend cycle even if the device is not bound. Acked-by: Bjorn Helgaas <bhelgaas@google.com> Tested-by: Peter Wu <peter@lekensteyn.nl> # Nvidia Optimus Tested-by: Lukas Wunner <lukas@wunner.de> # MacBook Pro Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> [lukas: add commit message, bikeshed code comments for clarity] Signed-off-by: Lukas Wunner <lukas@wunner.de> Link: https://patchwork.freedesktop.org/patch/msgid/92fb6e6ae2730915eb733c08e2f76c6a313e3860.1520068884.git.lukas@wunner.de |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.