From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 4B8C09862D3 for ; Mon, 4 Oct 2021 15:46:06 +0000 (UTC) From: Cornelia Huck In-Reply-To: <20211004110152-mutt-send-email-mst@kernel.org> References: <20210930012049.3780865-1-pasic@linux.ibm.com> <20210930070444-mutt-send-email-mst@kernel.org> <87fstm47no.fsf@redhat.com> <20211002141351-mutt-send-email-mst@kernel.org> <20211003070030.658fc94e.pasic@linux.ibm.com> <20211003021027-mutt-send-email-mst@kernel.org> <20211003032253-mutt-send-email-mst@kernel.org> <87ee912e45.fsf@redhat.com> <20211004083455-mutt-send-email-mst@kernel.org> <878rz83lx0.fsf@redhat.com> <20211004110152-mutt-send-email-mst@kernel.org> Date: Mon, 04 Oct 2021 17:45:06 +0200 Message-ID: <87zgro23r1.fsf@redhat.com> MIME-Version: 1.0 Subject: Re: [virtio-dev] Re: [RFC PATCH 1/1] virtio: write back features before verify Content-Type: text/plain To: "Michael S. Tsirkin" Cc: Halil Pasic , Jason Wang , Xie Yongji , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, markver@us.ibm.com, Christian Borntraeger , linux-s390@vger.kernel.org, virtio-dev@lists.oasis-open.org List-ID: On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: > On Mon, Oct 04, 2021 at 04:27:23PM +0200, Cornelia Huck wrote: >> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: >> >> > On Mon, Oct 04, 2021 at 02:01:14PM +0200, Cornelia Huck wrote: >> >> On Sun, Oct 03 2021, "Michael S. Tsirkin" wrote: >> >> > @@ -160,6 +163,33 @@ \subsection{Legacy Interface: A Note on Feature >> >> > Specification text within these sections generally does not apply >> >> > to non-transitional devices. >> >> > >> >> > +\begin{note} >> >> > +The device offers different features when used through >> >> > +the legacy interface and when operated in accordance with this >> >> > +specification. >> >> > +\end{note} >> >> > + >> >> > +Transitional drivers MUST use Devices only through the legacy interface >> >> >> >> s/Devices only through the legacy interface/devices through the legacy >> >> interface only/ >> >> >> >> ? >> > >> > Both versions are actually confused, since how do you >> > find out that device does not offer VIRTIO_F_VERSION_1? >> > >> > I think what this should really say is >> > >> > Transitional drivers MUST NOT accept VIRTIO_F_VERSION_1 through >> > the legacy interface. >> >> Ok, that makes sense. >> >> Would it make sense that transitional drivers MUST accept VERSION_1 >> through the non-legacy interface? Or is that redundant? > > We already have: > > A driver MUST accept VIRTIO_F_VERSION_1 if it is offered. Yep, so it is redundant. > > >> > >> > >> > Does linux actually satisfy this? Will it accept VIRTIO_F_VERSION_1 >> > through the legacy interface if offered? >> >> I think that the Linux drivers will not operate on feature bit 32+ if >> they are in legacy mode? > > > Well ... with PCI there's no *way* for host to set bit 32 through > legacy. But it might be possible with MMIO/CCW. Can you tell me > what happens then? ccw does not support accessing bit 32+, either. Not sure about mmio. > > >> >> >> >> Generally, looks good to me. >> > >> > Do we want to also add explanation that features can be >> > changed until FEATURES_OK? >> >> I always considered that to be implict, as feature negotiation is not >> over until we have FEATURES_OK. Not sure whether we need an extra note. > > Well Halil here says once you set a feature bit you can't clear it. > So maybe not ... Ok, so what about something like "If FEATURES_OK is not set, the driver MAY change the set of features it accepts." in the device initialization section? --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org