Re: [PATCH v2 4/5] vdpa: add new vdpa attribute VDPA_ATTR_DEV_F_VERSION_1

[Wu Zongyong]

On Tue, Sep 14, 2021 at 08:58:28AM -0400, Michael S. Tsirkin wrote:
> On Tue, Sep 14, 2021 at 08:24:51PM +0800, Wu Zongyong wrote:
> > This new attribute advertises whether the vdpa device is legacy or not.
> > Users can pick right virtqueue size if the vdpa device is legacy which
> > doesn't support to change virtqueue size.
> > 
> > Signed-off-by: Wu Zongyong <wuzongyong@xxxxxxxxxxxxxxxxx>
> 
> So if we are bothering with legacy, I think there are
> several things to do when building the interface
> - support transitional devices, that is allow userspace
>   to tell device it's in legacy mode
> - support reporting/setting supporting endian-ness

It's true if we try to implement a general drvier for legacy.
But this series is dedicated to implement a driver only for ENI. Is it
necessary to implement what you said here in this series?
> 
> > ---
> >  drivers/vdpa/vdpa.c          | 6 ++++++
> >  drivers/virtio/virtio_vdpa.c | 7 ++++++-
> >  include/uapi/linux/vdpa.h    | 1 +
> >  3 files changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> > index 1dc121a07a93..533d7f589eee 100644
> > --- a/drivers/vdpa/vdpa.c
> > +++ b/drivers/vdpa/vdpa.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/vdpa.h>
> >  #include <uapi/linux/vdpa.h>
> > +#include <uapi/linux/virtio_config.h>
> >  #include <net/genetlink.h>
> >  #include <linux/mod_devicetable.h>
> >  
> > @@ -494,6 +495,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
> >  	u16 max_vq_size;
> >  	u32 device_id;
> >  	u32 vendor_id;
> > +	u64 features;
> >  	void *hdr;
> >  	int err;
> >  
> > @@ -508,6 +510,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
> >  	device_id = vdev->config->get_device_id(vdev);
> >  	vendor_id = vdev->config->get_vendor_id(vdev);
> >  	max_vq_size = vdev->config->get_vq_num_max(vdev);
> > +	features = vdev->config->get_features(vdev);
> >  
> >  	err = -EMSGSIZE;
> >  	if (nla_put_string(msg, VDPA_ATTR_DEV_NAME, dev_name(&vdev->dev)))
> > @@ -520,6 +523,9 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
> >  		goto msg_err;
> >  	if (nla_put_u16(msg, VDPA_ATTR_DEV_MAX_VQ_SIZE, max_vq_size))
> >  		goto msg_err;
> > +	if (features & BIT_ULL(VIRTIO_F_VERSION_1) &&
> > +	    nla_put_flag(msg, VDPA_ATTR_DEV_VERSION_1))
> > +		goto msg_err;
> >  
> >  	genlmsg_end(msg, hdr);
> >  	return 0;
> > diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> > index 72eaef2caeb1..1cba957c4cdc 100644
> > --- a/drivers/virtio/virtio_vdpa.c
> > +++ b/drivers/virtio/virtio_vdpa.c
> > @@ -7,6 +7,7 @@
> >   *
> >   */
> >  
> > +#include "linux/virtio_config.h"
> >  #include <linux/init.h>
> >  #include <linux/module.h>
> >  #include <linux/device.h>
> > @@ -145,6 +146,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> >  	/* Assume split virtqueue, switch to packed if necessary */
> >  	struct vdpa_vq_state state = {0};
> >  	unsigned long flags;
> > +	bool may_reduce_num = false;
> >  	u32 align, num;
> >  	int err;
> >  
> > @@ -169,10 +171,13 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> >  		goto error_new_virtqueue;
> >  	}
> >  
> > +	if (ops->get_features(vdpa) & BIT_ULL(VIRTIO_F_VERSION_1))
> > +		may_reduce_num = true;
> > +
> >  	/* Create the vring */
> >  	align = ops->get_vq_align(vdpa);
> >  	vq = vring_create_virtqueue(index, num, align, vdev,
> > -				    true, true, ctx,
> > +				    true, may_reduce_num, ctx,
> >  				    virtio_vdpa_notify, callback, name);
> >  	if (!vq) {
> >  		err = -ENOMEM;
> > diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> > index 66a41e4ec163..ce0b74276a5b 100644
> > --- a/include/uapi/linux/vdpa.h
> > +++ b/include/uapi/linux/vdpa.h
> > @@ -32,6 +32,7 @@ enum vdpa_attr {
> >  	VDPA_ATTR_DEV_VENDOR_ID,		/* u32 */
> >  	VDPA_ATTR_DEV_MAX_VQS,			/* u32 */
> >  	VDPA_ATTR_DEV_MAX_VQ_SIZE,		/* u16 */
> > +	VDPA_ATTR_DEV_VERSION_1,		/* flag */
> >  
> >  	/* new attributes must be added above here */
> >  	VDPA_ATTR_MAX,
> > -- 
> > 2.31.1