netdev - Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

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Date:   Tue, 25 Aug 2020 12:09:51 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <olteanv@...il.com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

On Tue Aug 25 2020, Vladimir Oltean wrote:
> Hi Vinicius,
>
> On Mon, Aug 24, 2020 at 04:45:50PM -0700, Vinicius Costa Gomes wrote:
>> Kurt Kanzenbach <kurt@...utronix.de> writes:
>> >
>> > With TAPRIO traffic classes and the mapping to queues can be
>> > configured. The switch can also map traffic classes. That sounded like a
>> > good match to me.
>>
>> The only reason I could think that you would need this that *right now*
>> taprio has pretty glaring oversight: that in the offload parameters each entry
>> 'gate_mask' reference the "Traffic Class" (i.e. bit 0 is Traffic Class
>> 0), and it really should be the HW queue.
>>
>
> Sorry, but could you please explain why having the gate_mask reference
> the traffic classes is a glaring oversight, and how changing it would
> help here?
>
> Also, Kurt, could you please explain what the
> HR_PRTCCFG_PCP_TC_MAP_SHIFT field in HR_PRTCCFG is doing?
> To me, it appears that it's configuring ingress QoS classification on
> the port (and the reason why this is strange to me is because you're
> applying this configuration through an egress qdisc), but I want to make
> sure I'm not misunderstanding.

All the TSN operations in the switch such as the gate control work on
internally on traffic classes. The traffic class is determined by the
PCP field on the VLAN tagged frames. This mapping is configurable via
the pcp to tc map. And the TC also defines the hardware queue.

Thanks,
Kurt

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