From: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>,
Mikhail Golubev-Ciuchea <mikhail.golubev-ciuchea@opensynergy.com>,
virtio-comment@lists.oasis-open.org,
virtio-dev@lists.oasis-open.org, linux-can@vger.kernel.org,
Harald Mommer <harald.mommer@opensynergy.com>
Subject: [virtio-comment] Re: [virtio-dev] Re: [virtio-comment] [RFC PATCH v3] virtio-can: Device specification.
Date: Tue, 27 Feb 2024 10:02:33 +0100 [thread overview]
Message-ID: <Zd2lKYLGT8ZEFzZd@fedora> (raw)
In-Reply-To: <877circsh3.fsf@redhat.com>
On Mon, Feb 26, 2024 at 01:36:40PM +0100, Cornelia Huck wrote:
> On Wed, Feb 21 2024, Marc Kleine-Budde <mkl@pengutronix.de> wrote:
>
> > On 21.02.2024 14:16:54, Matias Ezequiel Vara Larsen wrote:
> >> On Wed, Feb 21, 2024 at 01:49:31PM +0100, Marc Kleine-Budde wrote:
> >> > On 21.02.2024 11:37:58, Matias Ezequiel Vara Larsen wrote:
> >> > > > > +The length of the \field{sdu} is determined by the \field{length}.
> >> > > > > +
> >> > > > > +The type of a CAN message identifier is determined by \field{flags}. The
> >> > > > > +3 most significant bits of \field{can_id} do not bear the information
> >> > > > > +about the type of the CAN message identifier and are 0.
> >> > > > > +
> >> > > > > +The device MUST reject any CAN frame type for which support has not been
> >> > > > > +negotiated with VIRTIO_CAN_RESULT_NOT_OK in \field{result} and MUST NOT
> >> > > > > +schedule the message for transmission. A CAN frame with an undefined bit
> >> > > > > +set in \field{flags} is treated like a CAN frame for which support has
> >> > > > > +not been negotiated.
> >> > > > > +
> >> > > > > +The device MUST reject any CAN frame for which \field{can_id} or
> >> > > > > +\field{sdu} length are out of range or the CAN controller is in an
> >> > > > > +invalid state with VIRTIO_CAN_RESULT_NOT_OK in \field{result} and MUST
> >> > > > > +NOT schedule the message for transmission.
> >> > > > > +
> >> > > I am not very familiar with CAN but how does the device figure out that
> >> > > the can_id is out of range?
> >> >
> >> > In classical CAN we have the standard CAN frames, which have an 11 bit
> >> > ID, and there are extended CAN frames, which have 29 bits ID. Extended
> >> > frames are signaled with VIRTIO_CAN_FLAGS_EXTENDED set.
> >> >
> >> > So if a standard frame uses more than 11 Bits of CAN-ID, it's considered
> >> > out of range.
> >
> > Another option would be an extended frame (VIRTIO_CAN_FLAGS_EXTENDED
> > set) and using more than 29 bits.
> >
> >> Thanks Marc for the explanation. Do you think that it would be
> >> worthwhile to add that to the spec at some point?
> >
> > Yes that makes sense as it clarifies what's meant by out of range for
> > CAN-IDs, for the valid length a reference to
> > \item[VIRTIO_CAN_F_CAN_CLASSIC (0)] and \item[VIRTIO_CAN_F_CAN_FD (1)]
> > might be added.
>
> [virtio mailing lists are supposedly down for migration right now, I
> hope there's some kind of backfill happening later...]
>
> If the question comes up, it does make sense to add a
> clarification... as the virtio-can spec is already voted upon and
> merged, we'd need a patch on top. Not sure if it would qualify as an
> editorial update or a vote would be needed, best to see it first :)
>
I will submit two patches regarding the changes proposed in this thread.
Matias
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next prev parent reply other threads:[~2024-02-27 9:02 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-09 14:22 [virtio-comment] [RFC PATCH v3] virtio-can: Device specification Mikhail Golubev-Ciuchea
2024-01-08 17:18 ` Mikhail Golubev-Ciuchea
2024-01-15 16:24 ` Cornelia Huck
2024-02-02 12:45 ` Cornelia Huck
2024-02-20 12:19 ` Matias Ezequiel Vara Larsen
2024-02-21 15:42 ` Mikhail Golubev-Ciuchea
2024-02-22 11:30 ` Matias Ezequiel Vara Larsen
2024-02-21 10:37 ` Matias Ezequiel Vara Larsen
[not found] ` <20240221-acts-decade-76d3d69e8e4d-mkl@pengutronix.de>
2024-02-21 13:16 ` [virtio-comment] Re: [virtio-dev] " Matias Ezequiel Vara Larsen
[not found] ` <20240221-juggling-uproar-9518b4901f41-mkl@pengutronix.de>
2024-02-26 12:36 ` Cornelia Huck
2024-02-27 9:02 ` Matias Ezequiel Vara Larsen [this message]
2024-02-13 14:57 ` [virtio-comment] Re: [virtio-dev] " Cornelia Huck
2024-02-16 11:08 ` Cornelia Huck
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