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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Dec 08, 2023 at 04:07:54PM +0900, 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@chromium.org>

tagged, thanks!
I'm still debating with myself whether we can classify this
as a bugfix ... better not risk it I guess.

> ---
> 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
>  
> -- 
> 2.43.0.472.g3155946c3a-goog