On Wednesday, August 31, 2016 08:15:18 AM Lukas Wunner wrote:
> There are devices not power-manageable by the platform, but still able
> to runtime suspend to D3cold with a nonstandard mechanism. One example
> is laptop hybrid graphics where the discrete GPU and its built-in HDA
> controller are power-managed either with a _DSM (AMD PowerXpress, Nvidia
> Optimus) or a separate gmux controller (MacBook Pro). Another example
> is Thunderbolt on Macs which is power-managed with custom ACPI methods.
>
> When putting the system to sleep, we currently handle such devices
> improperly by transitioning them from D3cold to D3hot (the default power
> state defined at the top of pci_target_state()). This wastes energy and
> prolongs the suspend sequence (powering up the Thunderbolt controller
> takes 2 seconds).
>
> Avoid that by assuming that a nonstandard PM mechanism is at work if the
> device is not platform-power-manageable but currently in D3cold.
>
> If the device is wakeup enabled, we might still have to wake it up from
> D3cold if PME cannot be signaled from that power state.
>
> The check for devices without PM capability comes before the check for
> D3cold since such devices could in theory also be powered down by
> nonstandard means and should then be afforded direct-complete as well.
>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> drivers/pci/pci.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index aab9d51..72a9d3a 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1959,9 +1959,22 @@ static pci_power_t pci_target_state(struct pci_dev *dev)
> default:
> target_state = state;
> }
> - } else if (!dev->pm_cap) {
> +
> + return target_state;
> + }
> +
> + if (!dev->pm_cap)
> target_state = PCI_D0;
> - } else if (device_may_wakeup(&dev->dev)) {
> +
> + /*
> + * If the device is in D3cold even though it's not power-manageable by
> + * the platform, it may have been powered down by nonstandard means.
> + * Best to let it slumber.
> + */
> + if (dev->current_state == PCI_D3cold)
> + target_state = PCI_D3cold;
> +
> + if (device_may_wakeup(&dev->dev)) {
> /*
> * Find the deepest state from which the device can generate
> * wake-up events, make it the target state and enable device
>
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