• Rafael J. Wysocki's avatar
    PCI: Restore config space on runtime resume despite being unbound · e2b3fa0c
    Rafael J. Wysocki authored
    [ Upstream commit 5775b843 ]
    
    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: default avatarBjorn 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: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    [lukas: add commit message, bikeshed code comments for clarity]
    Signed-off-by: default avatarLukas Wunner <lukas@wunner.de>
    Link: https://patchwork.freedesktop.org/patch/msgid/92fb6e6ae2730915eb733c08e2f76c6a313e3860.1520068884.git.lukas@wunner.deSigned-off-by: default avatarSasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    e2b3fa0c