linux-kernel - Re: [PATCH v2] virtio: Add support for no-reset virtio PCI PM

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Date:   Thu, 14 Dec 2023 10:47:50 +0100
From:   David Hildenbrand <david@...hat.com>
To:     David Stevens <stevensd@...omium.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] virtio: Add support for no-reset virtio PCI PM

On 08.12.23 08:07, David Stevens wrote:
> If a virtio_pci_device supports native PCI power management and has the
> No_Soft_Reset bit set, then skip resetting and reinitializing the device
> when suspending and restoring the device. This allows system-wide low
> power states like s2idle to be used in systems with stateful virtio
> devices that can't simply be re-initialized (e.g. virtio-fs).
> 
> Signed-off-by: David Stevens <stevensd@...omium.org>
> ---
> v1 -> v2:
>   - Check the No_Soft_Reset bit
> 
>   drivers/virtio/virtio_pci_common.c | 34 +++++++++++++++++++++++++++++-
>   1 file changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index c2524a7207cf..3a95ecaf12dc 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -492,8 +492,40 @@ static int virtio_pci_restore(struct device *dev)
>   	return virtio_device_restore(&vp_dev->vdev);
>   }
>   
> +static bool vp_supports_pm_no_reset(struct device *dev)
> +{
> +	struct pci_dev *pci_dev = to_pci_dev(dev);
> +	u16 pmcsr;
> +
> +	if (!pci_dev->pm_cap)
> +		return false;
> +
> +	pci_read_config_word(pci_dev, pci_dev->pm_cap + PCI_PM_CTRL, &pmcsr);
> +	if (PCI_POSSIBLE_ERROR(pmcsr)) {
> +		dev_err(dev, "Unable to query pmcsr");
> +		return false;
> +	}
> +
> +	return pmcsr & PCI_PM_CTRL_NO_SOFT_RESET;
> +}
> +
> +static int virtio_pci_suspend(struct device *dev)
> +{
> +	return vp_supports_pm_no_reset(dev) ? 0 : virtio_pci_freeze(dev);
> +}
> +
> +static int virtio_pci_resume(struct device *dev)
> +{
> +	return vp_supports_pm_no_reset(dev) ? 0 : virtio_pci_restore(dev);
> +}
> +
>   static const struct dev_pm_ops virtio_pci_pm_ops = {
> -	SET_SYSTEM_SLEEP_PM_OPS(virtio_pci_freeze, virtio_pci_restore)
> +	.suspend = virtio_pci_suspend,
> +	.resume = virtio_pci_resume,
> +	.freeze = virtio_pci_freeze,
> +	.thaw = virtio_pci_restore,
> +	.poweroff = virtio_pci_freeze,
> +	.restore = virtio_pci_restore,
>   };
>   #endif
>   

Am I correct with my assumption that this will make s2idle work with virtio-mem-pci as well?

Right now, all suspending is disabled, but really only s4/hibernate is problematic.

[root@...0 ~]# echo "s2idle" > /sys/power/mem_sleep
[root@...0 ~]# echo "mem" > /sys/power/state
[  101.822991] PM: suspend entry (s2idle)
[  101.828978] Filesystems sync: 0.004 seconds
[  101.831618] Freezing user space processes
[  101.834569] Freezing user space processes completed (elapsed 0.001 seconds)
[  101.836915] OOM killer disabled.
[  101.838072] Freezing remaining freezable tasks
[  101.841054] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[  101.843538] printk: Suspending console(s) (use no_console_suspend to debug)
[  101.957676] virtio_mem virtio0: save/restore not supported.
[  101.957683] virtio-pci 0000:00:02.0: PM: pci_pm_suspend(): virtio_pci_freeze+0x0/0x50 returns -1
[  101.957702] virtio-pci 0000:00:02.0: PM: dpm_run_callback(): pci_pm_suspend+0x0/0x170 returns -1
[  101.957718] virtio-pci 0000:00:02.0: PM: failed to suspend async: error -1


-- 
Cheers,

David / dhildenb