linux-kernel - Re: [PATCH 1/2] PCI/PM: refactor pci_pm_suspend

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Date:   Fri, 11 Mar 2022 19:33:21 +0100
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Rajvi Jingar <rajvi.jingar@...el.com>, <bhelgaas@...gle.com>
CC:     <david.e.box@...ux.intel.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] PCI/PM: refactor pci_pm_suspend_noirq()

On 2/24/2022 9:29 PM, Rajvi Jingar wrote:
> The state of the device is saved during pci_pm_suspend_noirq(), if it has
> not already been saved, regardless of the skip_bus_pm flag value. So
> skip_bus_pm check is removed before saving the device state.
>
> Signed-off-by: Rajvi Jingar <rajvi.jingar@...el.com>
> Suggested-by: David E. Box <david.e.box@...ux.intel.com>
> ---
>   drivers/pci/pci-driver.c | 15 ++-------------
>   1 file changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 588588cfda48..ac3f7e1676a9 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -834,20 +834,9 @@ static int pci_pm_suspend_noirq(struct device *dev)
>   		}
>   	}
>   
> -	if (pci_dev->skip_bus_pm) {
> -		/*
> -		 * 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.  The device should
> -		 * be in D0 at this point, but if it is a bridge, it may be
> -		 * necessary to save its state.
> -		 */

The comment is outdated, but the role of skip_bus_pm needs to be 
explained.  It only applies to the bridge with a child in D0 case now, 
because the other one has gone away, so I would put a new comment before 
the reworked check below.


> -		if (!pci_dev->state_saved)
> -			pci_save_state(pci_dev);
> -	} else if (!pci_dev->state_saved) {
> +	if (!pci_dev->state_saved) {
>   		pci_save_state(pci_dev);
> -		if (pci_power_manageable(pci_dev))

For example:

/*

  * If the device is a bridge with a child in D0 below it, it needs to 
stay in D0, so check

  * skip_bus_pm to avoid putting it into a low-power state in that case.

  */


> +		if (!pci_dev->skip_bus_pm && pci_power_manageable(pci_dev))
>   			pci_prepare_to_sleep(pci_dev);
>   	}
>