From: Gerd Hoffmann <kraxel@redhat.com> To: Keiichi Watanabe <keiichiw@chromium.org> Cc: virtio-dev@lists.oasis-open.org, "Linux Media Mailing List" <linux-media@vger.kernel.org>, "Alexandre Courbot" <acourbot@chromium.org>, "Alex Lau" <alexlau@chromium.org>, "Daniel Vetter" <daniel@ffwll.ch>, "Dylan Reid" <dgreid@chromium.org>, "David Staessens" <dstaessens@chromium.org>, "Dmitry Sepp" <dmitry.sepp@opensynergy.com>, "Enrico Granata" <egranata@google.com>, "Frediano Ziglio" <fziglio@redhat.com>, "Hans Verkuil" <hverkuil@xs4all.nl>, "Stéphane Marchesin" <marcheu@chromium.org>, "Pawel Osciak" <posciak@chromium.org>, spice-devel@lists.freedesktop.org, "David Stevens" <stevensd@chromium.org>, "Tomasz Figa" <tfiga@chromium.org>, uril@redhat.com, "Samiullah Khawaja" <samiullah.khawaja@opensynergy.com>, "Kiran Pawar" <kiran.pawar@opensynergy.com> Subject: Re: [PATCH v3 1/2] virtio-video: Add virtio video device specification Date: Thu, 27 Feb 2020 10:28:56 +0100 [thread overview] Message-ID: <20200227092856.p4kuh5dhh2tk3nnf@sirius.home.kraxel.org> (raw) In-Reply-To: <CAD90VcaTJh5MTRggpOmCK2LAryMHha2+7nPkFVTT8N8S06tf-A@mail.gmail.com> Hi, > Dmitry's virtio-video driver > https://patchwork.linuxtv.org/patch/61717/. > Once it becomes fully functional, I'll post a list of possible > improvements of protocol. Cool. Actually implementing things can find design problems in the protocol you didn't notice earlier. > > > +\begin{description} > > > +\item[\field{version}] is the protocol version that the device talks. > > > + The device MUST set this to 0. > > > > What is the intended use case for this? > > > > Given that virtio has feature flags to negotiate support for optional > > features and protocol extensions between driver and device, why do you > > think this is needed? > > While feature flags work well when we "extend" the protocol with an > optional feature, they don't when we want to "drop" or "modify" > features. > For example, I guess it'd be useful when we want: > * to abandon a non-optional command, > * to change a non-optional struct's layout,or > * to change the order of commands in which the device expects to be sent. > > Though it might be possible to handle these changes by feature flags, > I suspect the version number allow us to transition protocols more > smoothly. Feature flags can be mandatory, both device and driver can fail initialization when a specific feature is not supported by the other end. So in case we did screw up things so badly that we have to effectively start over (which I hope wouldn't be the case) we can add a VERSION_2 feature flag for a new set of commands with new structs and new semantics. With a feature flag both driver and device can choose whenever they want support v1 or v2 or both. With a version config field this is more limited, the device can't decide to support both. So the bonus points for a smooth transition go to the feature flags not the version field ;) cheers, Gerd
WARNING: multiple messages have this Message-ID (diff)
From: Gerd Hoffmann <kraxel@redhat.com> To: Keiichi Watanabe <keiichiw@chromium.org> Cc: virtio-dev@lists.oasis-open.org, "Linux Media Mailing List" <linux-media@vger.kernel.org>, "Alexandre Courbot" <acourbot@chromium.org>, "Alex Lau" <alexlau@chromium.org>, "Daniel Vetter" <daniel@ffwll.ch>, "Dylan Reid" <dgreid@chromium.org>, "David Staessens" <dstaessens@chromium.org>, "Dmitry Sepp" <dmitry.sepp@opensynergy.com>, "Enrico Granata" <egranata@google.com>, "Frediano Ziglio" <fziglio@redhat.com>, "Hans Verkuil" <hverkuil@xs4all.nl>, "Stéphane Marchesin" <marcheu@chromium.org>, "Pawel Osciak" <posciak@chromium.org>, spice-devel@lists.freedesktop.org, "David Stevens" <stevensd@chromium.org>, "Tomasz Figa" <tfiga@chromium.org>, uril@redhat.com, "Samiullah Khawaja" <samiullah.khawaja@opensynergy.com>, "Kiran Pawar" <kiran.pawar@opensynergy.com> Subject: [virtio-dev] Re: [PATCH v3 1/2] virtio-video: Add virtio video device specification Date: Thu, 27 Feb 2020 10:28:56 +0100 [thread overview] Message-ID: <20200227092856.p4kuh5dhh2tk3nnf@sirius.home.kraxel.org> (raw) In-Reply-To: <CAD90VcaTJh5MTRggpOmCK2LAryMHha2+7nPkFVTT8N8S06tf-A@mail.gmail.com> Hi, > Dmitry's virtio-video driver > https://patchwork.linuxtv.org/patch/61717/. > Once it becomes fully functional, I'll post a list of possible > improvements of protocol. Cool. Actually implementing things can find design problems in the protocol you didn't notice earlier. > > > +\begin{description} > > > +\item[\field{version}] is the protocol version that the device talks. > > > + The device MUST set this to 0. > > > > What is the intended use case for this? > > > > Given that virtio has feature flags to negotiate support for optional > > features and protocol extensions between driver and device, why do you > > think this is needed? > > While feature flags work well when we "extend" the protocol with an > optional feature, they don't when we want to "drop" or "modify" > features. > For example, I guess it'd be useful when we want: > * to abandon a non-optional command, > * to change a non-optional struct's layout,or > * to change the order of commands in which the device expects to be sent. > > Though it might be possible to handle these changes by feature flags, > I suspect the version number allow us to transition protocols more > smoothly. Feature flags can be mandatory, both device and driver can fail initialization when a specific feature is not supported by the other end. So in case we did screw up things so badly that we have to effectively start over (which I hope wouldn't be the case) we can add a VERSION_2 feature flag for a new set of commands with new structs and new semantics. With a feature flag both driver and device can choose whenever they want support v1 or v2 or both. With a version config field this is more limited, the device can't decide to support both. So the bonus points for a smooth transition go to the feature flags not the version field ;) cheers, Gerd --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
next prev parent reply other threads:[~2020-02-27 9:29 UTC|newest] Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-06 10:20 [PATCH v3 0/2] Virtio video device specification Keiichi Watanabe 2020-02-06 10:20 ` [virtio-dev] " Keiichi Watanabe 2020-02-06 10:20 ` [PATCH v3 1/2] virtio-video: Add virtio " Keiichi Watanabe 2020-02-06 10:20 ` [virtio-dev] " Keiichi Watanabe 2020-02-25 9:59 ` Gerd Hoffmann 2020-02-25 9:59 ` [virtio-dev] " Gerd Hoffmann 2020-02-27 7:24 ` Keiichi Watanabe 2020-02-27 7:24 ` [virtio-dev] " Keiichi Watanabe 2020-02-27 9:28 ` Gerd Hoffmann [this message] 2020-02-27 9:28 ` Gerd Hoffmann 2020-03-04 4:31 ` Alexandre Courbot 2020-03-04 4:31 ` [virtio-dev] " Alexandre Courbot 2020-03-04 6:42 ` Gerd Hoffmann 2020-03-04 6:42 ` [virtio-dev] " Gerd Hoffmann 2020-03-04 10:07 ` Alexandre Courbot 2020-03-04 10:07 ` [virtio-dev] " Alexandre Courbot 2020-03-23 12:07 ` Keiichi Watanabe 2020-03-23 12:07 ` [virtio-dev] " Keiichi Watanabe 2020-03-23 13:28 ` Dmitry Sepp 2020-03-23 13:28 ` [virtio-dev] " Dmitry Sepp 2020-03-23 15:48 ` Keiichi Watanabe 2020-03-23 15:48 ` [virtio-dev] " Keiichi Watanabe 2020-03-25 9:47 ` Dmitry Sepp 2020-03-25 9:47 ` [virtio-dev] " Dmitry Sepp 2020-03-27 3:35 ` Keiichi Watanabe 2020-03-27 3:35 ` [virtio-dev] " Keiichi Watanabe 2020-03-30 9:53 ` Dmitry Sepp 2020-03-30 9:53 ` [virtio-dev] " Dmitry Sepp 2020-04-06 9:32 ` Alexandre Courbot 2020-04-06 9:32 ` [virtio-dev] " Alexandre Courbot 2020-04-06 11:46 ` Keiichi Watanabe 2020-04-06 11:46 ` [virtio-dev] " Keiichi Watanabe 2020-04-07 9:21 ` Dmitry Sepp 2020-04-07 9:21 ` [virtio-dev] " Dmitry Sepp 2020-04-09 10:46 ` Keiichi Watanabe 2020-04-09 10:46 ` [virtio-dev] " Keiichi Watanabe 2020-04-17 8:08 ` Dmitry Sepp 2020-04-17 8:08 ` [virtio-dev] " Dmitry Sepp 2020-04-20 9:57 ` Keiichi Watanabe 2020-04-20 9:57 ` [virtio-dev] " Keiichi Watanabe 2020-04-21 8:38 ` Dmitry Sepp 2020-04-21 8:38 ` [virtio-dev] " Dmitry Sepp 2020-04-24 11:42 ` Keiichi Watanabe 2020-04-24 11:42 ` [virtio-dev] " Keiichi Watanabe 2020-04-27 14:28 ` Dmitry Sepp 2020-04-27 14:28 ` [virtio-dev] " Dmitry Sepp 2020-04-07 14:49 ` Dmitry Sepp 2020-04-07 14:49 ` [virtio-dev] " Dmitry Sepp 2020-04-09 10:46 ` Keiichi Watanabe 2020-04-09 10:46 ` [virtio-dev] " Keiichi Watanabe 2020-04-09 13:13 ` Dmitry Sepp 2020-04-09 13:13 ` [virtio-dev] " Dmitry Sepp 2020-04-24 11:45 ` Keiichi Watanabe 2020-04-24 11:45 ` [virtio-dev] " Keiichi Watanabe 2020-04-27 9:33 ` Dmitry Sepp 2020-04-27 9:33 ` [virtio-dev] " Dmitry Sepp 2020-05-18 5:17 ` Keiichi Watanabe 2020-05-18 5:17 ` [virtio-dev] " Keiichi Watanabe 2020-05-27 12:12 ` Dmitry Sepp 2020-05-27 12:12 ` [virtio-dev] " Dmitry Sepp 2020-05-29 14:21 ` Keiichi Watanabe 2020-05-29 14:21 ` [virtio-dev] " Keiichi Watanabe 2020-06-01 7:19 ` Alexandre Courbot 2020-06-01 7:19 ` [virtio-dev] " Alexandre Courbot 2020-02-06 10:20 ` [PATCH v3 2/2] virtio-video: Define a feature for exported objects from different virtio devices Keiichi Watanabe 2020-02-06 10:20 ` [virtio-dev] " Keiichi Watanabe 2020-02-25 10:01 ` Gerd Hoffmann 2020-02-25 10:01 ` [virtio-dev] " Gerd Hoffmann 2020-02-27 7:24 ` Keiichi Watanabe 2020-02-27 7:24 ` [virtio-dev] " Keiichi Watanabe
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