[virtio-comment] RE: [PATCH v5 0/7] Introduce device group and device management

From: Parav Pandit <parav@nvidia.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
	Max Gurtovoy <mgurtovoy@nvidia.com>
Cc: "jasowang@redhat.com" <jasowang@redhat.com>,
	"virtio-comment@lists.oasis-open.org"
	<virtio-comment@lists.oasis-open.org>,
	"cohuck@redhat.com" <cohuck@redhat.com>,
	"virtio-dev@lists.oasis-open.org"
	<virtio-dev@lists.oasis-open.org>, Oren Duer <oren@nvidia.com>,
	Shahaf Shuler <shahafs@nvidia.com>,
	"aadam@redhat.com" <aadam@redhat.com>,
	"virtio@lists.oasis-open.org" <virtio@lists.oasis-open.org>
Subject: [virtio-comment] RE: [PATCH v5 0/7] Introduce device group and device management
Date: Tue, 5 Jul 2022 15:11:43 +0000	[thread overview]
Message-ID: <PH0PR12MB5481D9416A601E6F2D4A32FFDC819@PH0PR12MB5481.namprd12.prod.outlook.com> (raw)
In-Reply-To: <20220705095514-mutt-send-email-mst@kernel.org>

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, July 5, 2022 9:57 AM
> 
> On Wed, Apr 27, 2022 at 01:58:17AM +0300, Max Gurtovoy wrote:
> > Hi,
> > A device group definition will help extending the virtio specefication
> > for various future features that require a notion of grouping devices
> > together or managing devices inside a group. A device group include one or
> more virtio devices.
> > For now, only support for type 1 device group was added.
> 
> How about posting a new version? I frankly think between the hardware
> hack I proposed and the new admin queue transport proposal, we do not
> need to work hard to save on writeable registers and so for starters at least
> we can just use feature bits instead of the query capability command.

Reader and writer via different channel is really a hack.
It still doesn't help to have efficient hw.

What is the technical reason to use feature bits which has strong relationships with device initialization sequence?
The proposed bits are AQ functionality bits and not per_say device feature bits?

This enables to build device in lot more flexible (and frankly simple way).
Looking at sw guest driver being simple to use existing limited 64-bits is just one part of it.

And when AQ exists, most of the plumbing comes for free.
So I fail to see the simplicity benefit of overloading feature bits for things that has no relation to device init sequence.

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