Re: [PATCH] PCI: PM: Skip devices in D0 for suspend-to-idle

[Rafael J. Wysocki]

On Thursday, June 13, 2019 12:14:02 AM CEST Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> Commit d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
> attempted to avoid a problem with devices whose drivers want them to
> stay in D0 over suspend-to-idle and resume, but it did not go as far
> as it should with that.
> 
> Namely, first of all, it is questionable to change the power state
> of a PCI bridge with a device in D0 under it, but that is not
> actively prevented from happening during system-wide PM transitions,
> so use the skip_bus_pm flag introduced by commit d491f2b75237 for
> that.
> 
> Second, the configuration of devices left in D0 (whatever the reason)
> during suspend-to-idle need not be changed and attempting to put them
> into D0 again by force may confuse some firmware, so explicitly avoid
> doing that.
> 
> Fixes: d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
> Reported-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> 
> Tested on Dell XPS13 9360 with no issues.
> 
> ---
>  drivers/pci/pci-driver.c |   47 +++++++++++++++++++++++++++++++++++------------
>  1 file changed, 35 insertions(+), 12 deletions(-)
> 
> Index: linux-pm/drivers/pci/pci-driver.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-driver.c
> +++ linux-pm/drivers/pci/pci-driver.c
> @@ -524,7 +524,6 @@ static void pci_pm_default_resume_early(
>  	pci_power_up(pci_dev);
>  	pci_restore_state(pci_dev);
>  	pci_pme_restore(pci_dev);
> -	pci_fixup_device(pci_fixup_resume_early, pci_dev);
>  }
>  
>  /*
> @@ -842,18 +841,16 @@ static int pci_pm_suspend_noirq(struct d
>  
>  	if (pci_dev->skip_bus_pm) {
>  		/*
> -		 * The function is running for the second time in a row without
> +		 * Either the device is a bridge with a child in D0 below it, or
> +		 * the function is running for the second time in a row without
>  		 * going through full resume, which is possible only during
> -		 * suspend-to-idle in a spurious wakeup case.  Moreover, the
> -		 * device was originally left in D0, so its power state should
> -		 * not be changed here and the device register values saved
> -		 * originally should be restored on resume again.
> +		 * suspend-to-idle in a spurious wakeup case.  The device should
> +		 * be in D0 at this point, but if it is a bridge, it may be
> +		 * necessary to save its state.
>  		 */
> -		pci_dev->state_saved = true;
> -	} else if (pci_dev->state_saved) {
> -		if (pci_dev->current_state == PCI_D0)
> -			pci_dev->skip_bus_pm = true;
> -	} else {
> +		if (!pci_dev->state_saved)
> +			pci_save_state(pci_dev);
> +	} else if (!pci_dev->state_saved) {
>  		pci_save_state(pci_dev);
>  		if (pci_power_manageable(pci_dev))
>  			pci_prepare_to_sleep(pci_dev);
> @@ -862,6 +859,22 @@ static int pci_pm_suspend_noirq(struct d
>  	dev_dbg(dev, "PCI PM: Suspend power state: %s\n",
>  		pci_power_name(pci_dev->current_state));
>  
> +	if (pci_dev->current_state == PCI_D0) {
> +		pci_dev->skip_bus_pm = true;
> +		/*
> +		 * Changing the power state of a PCI bridge with a device in D0
> +		 * below it is questionable, so avoid doing that by setting the
> +		 * skip_bus_pm flag for the parent bridge.
> +		 */
> +		if (pci_dev->bus->self)
> +			pci_dev->bus->self->skip_bus_pm = true;
> +	}
> +
> +	if (pci_dev->skip_bus_pm && !pm_suspend_via_firmware()) {
> +		dev_dbg(dev, "PCI PM: Skipped\n");
> +		goto Fixup;
> +	}
> +
>  	pci_pm_set_unknown_state(pci_dev);
>  
>  	/*
> @@ -909,7 +922,16 @@ static int pci_pm_resume_noirq(struct de
>  	if (dev_pm_smart_suspend_and_suspended(dev))
>  		pm_runtime_set_active(dev);
>  
> -	pci_pm_default_resume_early(pci_dev);
> +	/*
> +	 * In the suspend-to-idle case, devices left in D0 during suspend will
> +	 * stay in D0, so it is not necessary to restore or update their
> +	 * configuration here and attempting to put them into D0 again may
> +	 * confuse some firmware, so avoid doing that.
> +	 */
> +	if (!pci_dev->skip_bus_pm || pm_suspend_via_firmware())
> +		pci_pm_default_resume_early(pci_dev);
> +
> +	pci_fixup_device(pci_fixup_resume_early, pci_dev);
>  
>  	if (pci_has_legacy_pm_support(pci_dev))
>  		return pci_legacy_resume_early(dev);
> @@ -1200,6 +1222,7 @@ static int pci_pm_restore_noirq(struct d
>  	}
>  
>  	pci_pm_default_resume_early(pci_dev);
> +	pci_fixup_device(pci_fixup_resume_early, pci_dev);
>  
>  	if (pci_has_legacy_pm_support(pci_dev))
>  		return pci_legacy_resume_early(dev);
> 

Bjorn, please let me know if you have any reservations here.

Since this has been confirmed to fix a reported issue, I'm about to queue it up for 5.2-rc6.

Cheers,
Rafael