Date:   Tue, 21 Jan 2020 17:41:21 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...lanox.com>
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        <virtualization@...ts.linux-foundation.org>,
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        "maxime.coquelin@...hat.com" <maxime.coquelin@...hat.com>,
        "Liang, Cunming" <cunming.liang@...el.com>,
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Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus


On 2020/1/21 下午4:40, Tian, Kevin wrote:
>> From: Jason Wang <jasowang@...hat.com>
>> Sent: Friday, January 17, 2020 11:03 AM
>>
>>
>> On 2020/1/16 下午11:22, 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.
> the concept of VDEV includes both software bits and ADIs. If you
> only take about hardware types, using ADI is more accurate.


Ok.


>
>>>> - 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.
> ADI is just a term for minimally assignable resource in Scalable IOV.
> 'assignable' implies several things, e.g. the resource can be independently
> mapped to/accessed by user space or guest, DMAs between two
> ADIs are isolated, operating one ADI doesn't affecting another ADI,
> etc.  I'm not clear about  other vendor specific interfaces, but supposing
> they need match the similar requirements. Then do we really want to
> differentiate ADI vs. SF? What about merging them with ADI as just
> one example of finer-grained slicing?


I think so. That what Jason G want as well.

Thanks


>
>>
>>>> @@ -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@...hat.com>
>>> 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@...hat.com>"
>>>> +#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
>>>

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