On Wednesday, August 31, 2016 08:15:18 AM Lukas Wunner wrote:
> Commit 58a1fbbb2ee8 ("PM / PCI / ACPI: Kick devices that might have been
> reset by firmware") added a runtime resume for devices that were runtime
> suspended when the system entered sleep.
>
> The motivation was that devices might be in a reset-power-on state after
> waking from system sleep, so their power state as perceived by Linux
> (stored in pci_dev->current_state) would no longer reflect reality.
> By resuming such devices, we allow them to return to a low-power state
> via autosuspend and also bring their current_state in sync with reality.
>
> However for devices that are *not* in a reset-power-on state, doing an
> unconditional resume wastes energy. A more refined approach is called
> for which issues a runtime resume only if the power state after
> direct-complete is shallower than it was before. To achieve this, update
> the device's current_state by querying the platform firmware and reading
> its PMCSR.
>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> ---
> drivers/pci/pci-driver.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index e39a67c..fd4b9c4 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -684,8 +684,19 @@ static int pci_pm_prepare(struct device *dev)
>
> static void pci_pm_complete(struct device *dev)
> {
> - pci_dev_complete_resume(to_pci_dev(dev));
> - pm_complete_with_resume_check(dev);
> + struct pci_dev *pci_dev = to_pci_dev(dev);
> +
> + pci_dev_complete_resume(pci_dev);
> + pm_generic_complete(dev);
> +
> + /* Resume device if platform firmware has put it in reset-power-on */
> + if (dev->power.direct_complete && pm_resume_via_firmware()) {
> + pci_power_t pre_sleep_state = pci_dev->current_state;
> +
> + pci_update_current_state(pci_dev, pci_dev->current_state);
I'm not sure if this can be made reliable enough for all of the systems out
there (including the pre-ACPI-4.0 ones and so on). I'm a bit concerned that
we'll uncover firmware issues and such by doing this.
How much of a problem the existing code is in practice?
> + if (pci_dev->current_state < pre_sleep_state)
> + pm_request_resume(dev);
> + }
> }
>
> #else /* !CONFIG_PM_SLEEP */
>
Thanks,
Rafael
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