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Date: Thu, 18 Apr 2024 03:34:10 -0400
From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Zhu, Lingshan" <lingshan.zhu@intel.com>
Cc: David Stevens <stevensd@chromium.org>, Jason Wang <jasowang@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Eugenio Perez <eperezma@redhat.com>,
	virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 1/1] virtio: Add support for the virtio suspend feature
Message-ID: <20240418033313-mutt-send-email-mst@kernel.org>
References: <20240417085440.4036535-1-stevensd@chromium.org>
 <20240417085440.4036535-2-stevensd@chromium.org>
 <a123f8da-a6b9-4923-95ff-7814804cdabb@intel.com>
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In-Reply-To: <a123f8da-a6b9-4923-95ff-7814804cdabb@intel.com>

On Thu, Apr 18, 2024 at 03:14:37PM +0800, Zhu, Lingshan wrote:
> 
> 
> On 4/17/2024 4:54 PM, David Stevens wrote:
> > Add support for the VIRTIO_F_SUSPEND feature. When this feature is
> > negotiated, power management can use it to suspend virtio devices
> > instead of resorting to resetting the devices entirely.
> > 
> > Signed-off-by: David Stevens <stevensd@chromium.org>
> > ---
> >   drivers/virtio/virtio.c            | 32 ++++++++++++++++++++++++++++++
> >   drivers/virtio/virtio_pci_common.c | 29 +++++++++++----------------
> >   drivers/virtio/virtio_pci_modern.c | 19 ++++++++++++++++++
> >   include/linux/virtio.h             |  2 ++
> >   include/uapi/linux/virtio_config.h | 10 +++++++++-
> >   5 files changed, 74 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index f4080692b351..cd11495a5098 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -1,5 +1,6 @@
> >   // SPDX-License-Identifier: GPL-2.0-only
> >   #include <linux/virtio.h>
> > +#include <linux/delay.h>
> >   #include <linux/spinlock.h>
> >   #include <linux/virtio_config.h>
> >   #include <linux/virtio_anchor.h>
> > @@ -580,6 +581,37 @@ int virtio_device_restore(struct virtio_device *dev)
> >   	return ret;
> >   }
> >   EXPORT_SYMBOL_GPL(virtio_device_restore);
> > +
> > +static int virtio_device_set_suspend_bit(struct virtio_device *dev, bool enabled)
> > +{
> > +	u8 status, target;
> > +
> > +	status = dev->config->get_status(dev);
> > +	if (enabled)
> > +		target = status | VIRTIO_CONFIG_S_SUSPEND;
> > +	else
> > +		target = status & ~VIRTIO_CONFIG_S_SUSPEND;
> > +	dev->config->set_status(dev, target);
> I think it is better to verify whether the device SUSPEND bit is
> already set or clear, we can just return if status == target.
> 
> Thanks
> Zhu Lingshan
> > +
> > +	while ((status = dev->config->get_status(dev)) != target) {
> > +		if (status & VIRTIO_CONFIG_S_NEEDS_RESET)
> > +			return -EIO;
> > +		mdelay(10);

Bad device state (set by surprise removal) should also
be handled here I think.


> > +	}
> > +	return 0;
> > +}
> > +
> > +int virtio_device_suspend(struct virtio_device *dev)
> > +{
> > +	return virtio_device_set_suspend_bit(dev, true);
> > +}
> > +EXPORT_SYMBOL_GPL(virtio_device_suspend);
> > +
> > +int virtio_device_resume(struct virtio_device *dev)
> > +{
> > +	return virtio_device_set_suspend_bit(dev, false);
> > +}
> > +EXPORT_SYMBOL_GPL(virtio_device_resume);
> >   #endif
> >   static int virtio_init(void)
> > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > index b655fccaf773..4d542de05970 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -495,31 +495,26 @@ 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)
> > +static int virtio_pci_suspend(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;
> > -	}
> > +	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
> > -	return pmcsr & PCI_PM_CTRL_NO_SOFT_RESET;
> > -}
> > +	if (virtio_has_feature(&vp_dev->vdev, VIRTIO_F_SUSPEND))
> > +		return virtio_device_suspend(&vp_dev->vdev);
> > -static int virtio_pci_suspend(struct device *dev)
> > -{
> > -	return vp_supports_pm_no_reset(dev) ? 0 : virtio_pci_freeze(dev);
> > +	return virtio_pci_freeze(dev);
> >   }
> >   static int virtio_pci_resume(struct device *dev)
> >   {
> > -	return vp_supports_pm_no_reset(dev) ? 0 : virtio_pci_restore(dev);
> > +	struct pci_dev *pci_dev = to_pci_dev(dev);
> > +	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
> > +
> > +	if (virtio_has_feature(&vp_dev->vdev, VIRTIO_F_SUSPEND))
> > +		return virtio_device_resume(&vp_dev->vdev);
> > +
> > +	return virtio_pci_restore(dev);
> >   }
> >   static const struct dev_pm_ops virtio_pci_pm_ops = {
> > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > index f62b530aa3b5..ac8734526b8d 100644
> > --- a/drivers/virtio/virtio_pci_modern.c
> > +++ b/drivers/virtio/virtio_pci_modern.c
> > @@ -209,6 +209,22 @@ static void vp_modern_avq_deactivate(struct virtio_device *vdev)
> >   	__virtqueue_break(admin_vq->info.vq);
> >   }
> > +static bool vp_supports_pm_no_reset(struct pci_dev *pci_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(&pci_dev->dev, "Unable to query pmcsr");
> > +		return false;
> > +	}
> > +
> > +	return pmcsr & PCI_PM_CTRL_NO_SOFT_RESET;
> > +}
> > +
> >   static void vp_transport_features(struct virtio_device *vdev, u64 features)
> >   {
> >   	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> > @@ -223,6 +239,9 @@ static void vp_transport_features(struct virtio_device *vdev, u64 features)
> >   	if (features & BIT_ULL(VIRTIO_F_ADMIN_VQ))
> >   		__virtio_set_bit(vdev, VIRTIO_F_ADMIN_VQ);
> > +
> > +	if (features & BIT_ULL(VIRTIO_F_SUSPEND) && vp_supports_pm_no_reset(pci_dev))
> > +		__virtio_set_bit(vdev, VIRTIO_F_SUSPEND);
> >   }
> >   static int __vp_check_common_size_one_feature(struct virtio_device *vdev, u32 fbit,
> > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > index b0201747a263..8e456b04114e 100644
> > --- a/include/linux/virtio.h
> > +++ b/include/linux/virtio.h
> > @@ -160,6 +160,8 @@ void virtio_config_changed(struct virtio_device *dev);
> >   #ifdef CONFIG_PM_SLEEP
> >   int virtio_device_freeze(struct virtio_device *dev);
> >   int virtio_device_restore(struct virtio_device *dev);
> > +int virtio_device_suspend(struct virtio_device *dev);
> > +int virtio_device_resume(struct virtio_device *dev);
> >   #endif
> >   void virtio_reset_device(struct virtio_device *dev);
> > diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> > index 2445f365bce7..4a6e2c28ea76 100644
> > --- a/include/uapi/linux/virtio_config.h
> > +++ b/include/uapi/linux/virtio_config.h
> > @@ -40,6 +40,8 @@
> >   #define VIRTIO_CONFIG_S_DRIVER_OK	4
> >   /* Driver has finished configuring features */
> >   #define VIRTIO_CONFIG_S_FEATURES_OK	8
> > +/* Driver has suspended the device */
> > +#define VIRTIO_CONFIG_S_SUSPEND		0x10
> >   /* Device entered invalid state, driver must reset it */
> >   #define VIRTIO_CONFIG_S_NEEDS_RESET	0x40
> >   /* We've given up on this device. */
> > @@ -52,7 +54,7 @@
> >    * rest are per-device feature bits.
> >    */
> >   #define VIRTIO_TRANSPORT_F_START	28
> > -#define VIRTIO_TRANSPORT_F_END		42
> > +#define VIRTIO_TRANSPORT_F_END		43
> >   #ifndef VIRTIO_CONFIG_NO_LEGACY
> >   /* Do we get callbacks when the ring is completely used, even if we've
> > @@ -120,4 +122,10 @@
> >    */
> >   #define VIRTIO_F_ADMIN_VQ		41
> > +/*
> > + * This feature indicates that the driver can suspend the device via the
> > + * suspend bit in the device status byte.
> > + */
> > +#define VIRTIO_F_SUSPEND		42
> > +
> >   #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */