Re: [PATCH v1] virtio-can: define out of rage can-id and sdu

[Matias Ezequiel Vara Larsen <mvaralar@redhat.com>]

On Thu, Jun 27, 2024 at 03:16:35PM +0200, Harald Mommer wrote:
> 
> On 27.06.24 13:08, Matias Ezequiel Vara Larsen wrote:
> > Explain when a message is out of range.
> > 
> > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
> > ---
> > v0 -> v1
> >      * Use length of the field wording to indicate out of range
> >      * Add when sdu length is out of range
> > ---
> >   device-types/can/description.tex | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> > 
> > diff --git a/device-types/can/description.tex b/device-types/can/description.tex
> > index 2511d9c..fa56abd 100644
> > --- a/device-types/can/description.tex
> > +++ b/device-types/can/description.tex
> > @@ -191,6 +191,14 @@ \subsubsection{Controller Mode}\label{sec:Device Types / CAN Device / Device Ope
> >   invalid state with VIRTIO_CAN_RESULT_NOT_OK in \field{result} and MUST
> >   NOT schedule the message for transmission.
> > +Note that the \field{can_id} field of a CAN frame is out of range when its
> > +length is more than 11 bits for standard frames or more than 29 bits for
> > +extended frames. The length of the \field{sdu} field is out of range when it
> > +uses more than 8 bytes for standard frames. If the VIRTIO_CAN_F_CAN_FD feature
> > +has been negotiated, the lenght of the \field{sdu} field is out of range when
> > +it uses more than 8 bytes and is not in the set [ 12, 16, 20, 24, 32, 48, 64 ]
> > +bytes.
> > +
> >   If the parameters are valid the message is scheduled for transmission.
> >   If feature VIRTIO_CAN_F_CAN_LATE_TX_ACK has been negotiated the
> > 
> > base-commit: 37c6a406678a5ee891fdf5671298cb4fcfa517f2
> 
> "If the VIRTIO_CAN_F_CAN_FD feature has been negotiated, ..."
> 
> Would mean that sending a CAN classic frame having an sdu length > 8 over a
> virtio CAN device capable to send also CAN FD frames would be allowed. This
> is not the case. The condition is the type of the actual CAN frame to be
> sent.
> 
> Decisive for CAN classic / CAN FD is the presence or absence of
> VIRTIO_CAN_FLAGS_FD in the flags.
> 
> Having an automatism to change a CAN classic frame to a CAN FD frame or the
> other way around under some conditions is not in the spec.
> 
> For example: "If the VIRTIO_CAN_FLAGS_FD bit is set in the \field{flags},
> ..."
> 
> Or "If the frame is a CAN FD frame, ..."
> 
> 

Thanks Harald, I will add it to v2.

Matias