Re: [PATCH 3/5] vDPA: introduce vDPA bus

[Jason Wang]

On 2020/1/16 äå11:22, Jason Gunthorpe wrote:
> On Thu, Jan 16, 2020 at 08:42:29PM +0800, Jason Wang wrote:
> > vDPA device is a device that uses a datapath which complies with the
> > virtio specifications with vendor specific control path. vDPA devices
> > can be both physically located on the hardware or emulated by
> > software. vDPA hardware devices are usually implemented through PCIE
> > with the following types:
> >
> > - PF (Physical Function) - A single Physical Function
> > - VF (Virtual Function) - Device that supports single root I/O
> >    virtualization (SR-IOV). Its Virtual Function (VF) represents a
> >    virtualized instance of the device that can be assigned to different
> >    partitions
> > - VDEV (Virtual Device) - With technologies such as Intel Scalable
> >    IOV, a virtual device composed by host OS utilizing one or more
> >    ADIs.
> > - SF (Sub function) - Vendor specific interface to slice the Physical
> >    Function to multiple sub functions that can be assigned to different
> >    partitions as virtual devices.
> I really hope we don't end up with two different ways to spell this
> same thing.


I think you meant ADI vs SF. It looks to me that ADI is limited to the 
scope of scalable IOV but SF not.


> > @@ -0,0 +1,2 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +obj-$(CONFIG_VDPA) += vdpa.o
> > diff --git a/drivers/virtio/vdpa/vdpa.c b/drivers/virtio/vdpa/vdpa.c
> > new file mode 100644
> > index 000000000000..2b0e4a9f105d
> > +++ b/drivers/virtio/vdpa/vdpa.c
> > @@ -0,0 +1,141 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * vDPA bus.
> > + *
> > + * Copyright (c) 2019, Red Hat. All rights reserved.
> > + *     Author: Jason Wang <jasowang@xxxxxxxxxx>
> 2020 tests days


Will fix.


> > + *
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/idr.h>
> > +#include <linux/vdpa.h>
> > +
> > +#define MOD_VERSION  "0.1"
> I think module versions are discouraged these days


Will remove.


> > +#define MOD_DESC     "vDPA bus"
> > +#define MOD_AUTHOR   "Jason Wang <jasowang@xxxxxxxxxx>"
> > +#define MOD_LICENSE  "GPL v2"
> > +
> > +static DEFINE_IDA(vdpa_index_ida);
> > +
> > +struct device *vdpa_get_parent(struct vdpa_device *vdpa)
> > +{
> > +	return vdpa->dev.parent;
> > +}
> > +EXPORT_SYMBOL(vdpa_get_parent);
> > +
> > +void vdpa_set_parent(struct vdpa_device *vdpa, struct device *parent)
> > +{
> > +	vdpa->dev.parent = parent;
> > +}
> > +EXPORT_SYMBOL(vdpa_set_parent);
> > +
> > +struct vdpa_device *dev_to_vdpa(struct device *_dev)
> > +{
> > +	return container_of(_dev, struct vdpa_device, dev);
> > +}
> > +EXPORT_SYMBOL_GPL(dev_to_vdpa);
> > +
> > +struct device *vdpa_to_dev(struct vdpa_device *vdpa)
> > +{
> > +	return &vdpa->dev;
> > +}
> > +EXPORT_SYMBOL_GPL(vdpa_to_dev);
> Why these trivial assessors? Seems unnecessary, or should at least be
> static inlines in a header


Will fix.


> > +int register_vdpa_device(struct vdpa_device *vdpa)
> > +{
> Usually we want to see symbols consistently prefixed with vdpa_*, is
> there a reason why register/unregister are swapped?


I follow the name from virtio. I will switch to vdpa_*.


> > +	int err;
> > +
> > +	if (!vdpa_get_parent(vdpa))
> > +		return -EINVAL;
> > +
> > +	if (!vdpa->config)
> > +		return -EINVAL;
> > +
> > +	err = ida_simple_get(&vdpa_index_ida, 0, 0, GFP_KERNEL);
> > +	if (err < 0)
> > +		return -EFAULT;
> > +
> > +	vdpa->dev.bus = &vdpa_bus;
> > +	device_initialize(&vdpa->dev);
> IMHO device_initialize should not be called inside something called
> register, toooften we find out that the caller drivers need the device
> to be initialized earlier, ie to use the kref, or something.
>
> I find the best flow is to have some init function that does the
> device_initialize and sets the device_name that the driver can call
> early.


Ok, will do.


> Shouldn't there be a device/driver matching process of some kind?


The question is what do we want do match here.

1) "virtio" vs "vhost", I implemented matching method for this in mdev 
series, but it looks unnecessary for vDPA device driver to know about 
this. Anyway we can use sysfs driver bind/unbind to switch drivers
2) virtio device id and vendor id. I'm not sure we need this consider 
the two drivers so far (virtio/vhost) are all bus drivers.

Thanks


> Jason