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Subject: Re: [v1,net-next, 1/2] ethtool: add setting frame preemption of
 traffic classes
To:     Vinicius Costa Gomes <vinicius.gomes@intel.com>,
        Vladimir Oltean <olteanv@gmail.com>
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From:   Murali Karicheri <m-karicheri2@ti.com>
Message-ID: <b1ef134d-e275-439f-f7a1-038537af4855@ti.com>
Date:   Tue, 25 Feb 2020 12:55:59 -0500
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Hi Vinicius,

On 02/11/2020 02:22 PM, Vinicius Costa Gomes wrote:
> Murali Karicheri <m-karicheri2@ti.com> 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