From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: From: Cornelia Huck In-Reply-To: References: <20220426225824.5918-1-mgurtovoy@nvidia.com> <20220426225824.5918-3-mgurtovoy@nvidia.com> <20220515111056-mutt-send-email-mst@kernel.org> Date: Tue, 17 May 2022 12:08:25 +0200 Message-ID: <87zgjgfp46.fsf@redhat.com> MIME-Version: 1.0 Subject: [virtio-dev] Re: [virtio-comment] RE: [PATCH v5 2/7] Introduce admin command set Content-Type: text/plain To: Parav Pandit , "Michael S. Tsirkin" , Max Gurtovoy Cc: "jasowang@redhat.com" , "virtio-comment@lists.oasis-open.org" , "virtio-dev@lists.oasis-open.org" , Oren Duer , Shahaf Shuler , "aadam@redhat.com" , "virtio@lists.oasis-open.org" List-ID: On Mon, May 16 2022, Parav Pandit wrote: > Hi Michael, > >> From: Michael S. Tsirkin >> Sent: Sunday, May 15, 2022 11:24 AM > > [..] > >> > +\subsection{VIRTIO ADMIN DEVICE CAPS ACCEPT >> command}\label{sec:Basic >> > +Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN >> > +DEVICE CAPS ACCEPT command} >> > + >> > +The VIRTIO_ADMIN_DEVICE_CAPS_ACCEPT command is used by the >> driver to acknowledge those admin capabilities it understands and wishes to >> use. >> >> >> ok so we have a protocol here, kind of like feature negotiation. Please write >> its description. >> e.g. is it ok to change accepted caps? when? can device change its caps etc >> etc etc. >> >> Avoiding this kind of spec work is exactly why me and jason keep telling you >> to consider just using features instead. Add a 64 bit admin features field to >> the PCI transport and be done with it. CCW and MMIO already have feature >> selector so it's trivial to add feature bits. >> > As we begin to scale with the device, adding more and more registers like this demands more on-device real estate to comply to the PCI standards. > > And therefore, things are queried/accessed rare or occasionally, are better accessed via a queue interface. > > One can argue that admin VQ is proposed only for the mgmt. functions so having this cfg register for PF is enough. > > However, AQ may find some usage in the VF/SF themselves down the road. > Hence, keeping the cap exchange transport this way is more optimal. > > Max has called out this AQ rationale in 4 or 5 points in the cover letter. I'm not against using a queue, but why not use feature bits for capabilities? As Michael said, the infrastructure for that is already in place. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org