Re: [v1,net-next, 1/2] ethtool: add setting frame preemption of traffic classes

[Murali Karicheri]

Hi Vinicius,

On 02/11/2020 02:22 PM, Vinicius Costa Gomes wrote:
> Murali Karicheri <m-karicheri2@xxxxxx> writes:
>
> > We are still working to send a patch for taprio offload on our hardware
> > and it may take a while to get to this. So if someone can help to add
> > the required kernel/driver interface for this, that will be great!
>
> Will add this to my todo list. But if anyone else has the spare cycles
> feel free to have a go at it.
Thanks! We have made some progress in sending the base driver to netdev
list now https://lkml.org/lkml/2020/2/22/157

This device is taprio offload capable. Next step is to add taprio
offload to this driver. Then other features will follow.

> > > > >        - ConfigChangeError - Error in configuration (AdminBaseTime <
> > > > >          CurrentTime)
> > > >
> > > > This can be exported similarly.
> > >
> > > In my view, having this as a "runtime" error is not useful, as we can
> > > verify this at configuration time.
> >
> > Looks like this is not an error per 802.1Q standard if I understood it
> > correctly.
> >
> > This is what I see.
> > =======================================================================
> >   From 802.1Q 2018, 8.6.9.1.1 SetCycleStartTime()
> >
> > If AdminBaseTime is set to the same time in the past in all bridges and
> > end stations, OperBaseTime is always in the past, and all cycles start
> > synchronized. Using AdminBaseTime in the past is appropriate when you
> > can start schedules prior to starting the application that uses the
> > schedules. Use of AdminBaseTime in the future is intended to change a
> > currently running schedule in all bridges and end stations to a new
> > schedule at a future time. Using AdminBaseTime in the future is
> > appropriate when schedules must be changed without stopping the
> > application
> > ========================================================================
>
> What I meant here is the case that I already have an "oper" schedule
> running, so my "oper->base_time" is in the past, and I try to add an
> "admin" schedule with a "base_time" also in the past. What's the
> expected behavior in this case? The text about stopping/starting
> applications doesn't seem to apply to the way the tc subsystem interacts
> with the applications.
> I try to add an "admin" schedule with a "base_time" also in the past.
> What's the expected behavior in this case?

Ok got it. I don't think this behavior is explained in the spec. I would
assume a sane thing to do is to switch to admin schedule if 
admin->base_time is newer than oper->base_time and flag
the ConfigChangeError to be compliant to the spec, but frankly speaking
I don't know how application is going to use this. It is a low priority
item IMO and can be added as needed.

Regards,

Murali
> > > > >        - SupportedListMax - Maximum supported Admin/Open shed list.
> > > > >
> > > > > Is there a plan to export these from driver through tc show or such
> > > > > command? The reason being, there would be applications developed to
> > > > > manage configuration/schedule of TSN nodes that would requires these
> > > > > information from the node. So would need a support either in tc or
> > > > > some other means to retrieve them from hardware or driver. That is my
> > > > > understanding...
> > >
> > > Hm, now I understamd what you meant here...
> > >
> > > > Not sure what answer you expect to receive for "is there any plan".
> > > > You can go ahead and propose something, as long as it is reasonably
> > > > useful to have.
> > >
> > > ... if this is indeed useful, perhaps one way to do is to add a subcommand
> > > to TC_SETUP_QDISC_TAPRIO, so we can retrieve the stats/information we want
> > > from the driver. Similar to what cls_flower does.
> >
> > What I understand is that there will be some work done to allow auto
> > configuration of TSN nodes from user space and that would need access to
> > all or some of the above parameters along with tc command to configure
> > the same. May be a open source project for this or some custom
> > application? Any such projects existing??
>
> Yeah, this is a big missing piece for TSN. I've heard 'netopeer2' and
> 'sysrepo' mentioned when similar questions were asked, but I have still
> to take a look at them and see what's missing. (Or if they are the right
> tool for the job)

--
Murali Karicheri
Texas Instruments