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Message-ID: References: <20230609142243.199074-1-Mikhail.Golubev-Ciuchea@opensynergy.com> <20240221-acts-decade-76d3d69e8e4d-mkl@pengutronix.de> <20240221-juggling-uproar-9518b4901f41-mkl@pengutronix.de> <877circsh3.fsf@redhat.com> Precedence: bulk X-Mailing-List: linux-can@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 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