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Date:   Thu, 18 Aug 2022 17:05:53 +0200
From:   Michael Walle <michael@walle.cc>
To:     Vladimir Oltean <vladimir.oltean@nxp.com>
Cc:     devicetree@vger.kernel.org, netdev@vger.kernel.org,
        Shawn Guo <shawnguo@kernel.org>, Leo Li <leoyang.li@nxp.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH devicetree 0/3] NXP LS1028A DT changes for multiple switch
 CPU ports
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References: <20220818140519.2767771-1-vladimir.oltean@nxp.com>
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 <20220818145556.ieg37btfny3o2i4q@skbuf>
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Am 2022-08-18 16:55, schrieb Vladimir Oltean:
> On Thu, Aug 18, 2022 at 04:49:49PM +0200, Michael Walle wrote:
>> Is it used automatically or does the userspace has to configure 
>> something?
> 
> DSA doesn't yet support multiple CPU ports, but even when it will, the
> second DSA master still won't be used automatically. If you want more
> details about the proposed UAPI to use the second CPU port, see here:
> https://patchwork.kernel.org/project/netdevbpf/cover/20220523104256.3556016-1-olteanv@gmail.com/
> 
>> > Care has been taken that this change does not produce regressions when
>> > using updated device trees with old kernels that do not support multiple
>> > DSA CPU ports. The only difference for old kernels will be the
>> > appearance of a new net device (for &enetc_port3) which will not be very
>> > useful for much of anything.
>> 
>> Mh, I don't understand. Does it now cause regressions or not? I mean
>> besides that there is a new unused interface?
> 
> It didn't cause regressions until kernel 5.13 when commit adb3dccf090b
> ("net: dsa: felix: convert to the new .change_tag_protocol DSA API")
> happened, then commit 00fa91bc9cc2 ("net: dsa: felix: fix tagging
> protocol changes with multiple CPU ports") fixed that regression and 
> was
> backported to the linux-5.15.y stable branch AFAIR. So at least kernels
> 5.15 and newer should work properly with the new device trees.

Thanks for the details!

>> I was just thinking of that systemready stuff where the u-boot might
>> supply its (newer) device tree to an older kernel, i.e. an older 
>> debian
>> or similar.
>> 
>> -michael
> 
> Yeah, I hear you, I'm doing my best to make the driver work with a
> one-size-fits-all device tree, both ways around.

TBH I don't really care much, I was merely curious what to expect.

-michael