netdev - Re: [PATCH net-next 5/5] net: dsa: mv88e6xxx: implementation of dynamic ATU entries

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Date:   Sat, 04 Feb 2023 09:48:24 +0100
From:   netdev@...io-technology.com
To:     Simon Horman <simon.horman@...igine.com>
Cc:     Vladimir Oltean <olteanv@...il.com>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        "maintainer:MICROCHIP KSZ SERIES ETHERNET SWITCH DRIVER" 
        <UNGLinuxDriver@...rochip.com>, Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Clément Léger <clement.leger@...tlin.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Russell King <linux@...linux.org.uk>,
        Christian Marangi <ansuelsmth@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        "open list:RENESAS RZ/N1 A5PSW SWITCH DRIVER" 
        <linux-renesas-soc@...r.kernel.org>,
        "moderated list:ETHERNET BRIDGE" <bridge@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next 5/5] net: dsa: mv88e6xxx: implementation of
 dynamic ATU entries

On 2023-02-04 09:12, Simon Horman wrote:
> On Fri, Feb 03, 2023 at 10:44:22PM +0200, Vladimir Oltean wrote:
>> On Fri, Feb 03, 2023 at 09:20:22AM +0100, Simon Horman wrote:
>> > > else if (someflag)
>> > >         dosomething();
>> > >
>> > > For now only one flag will actually be set and they are mutually exclusive,
>> > > as they will not make sense together with the potential flags I know, but
>> > > that can change at some time of course.
>> >
>> > Yes, I see that is workable. I do feel that checking for other flags would
>> > be a bit more robust. But as you say, there are none. So whichever
>> > approach you prefer is fine by me.
>> 
>> The model we have for unsupported bits in the 
>> SWITCHDEV_ATTR_ID_PORT_PRE_BRIDGE_FLAGS
>> and SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS handlers is essentially this:
>> 
>> 	if (flags & ~(supported_flag_mask))
>> 		return -EOPNOTSUPP;
>> 
>> 	if (flags & supported_flag_1)
>> 		...
>> 
>> 	if (flags & supported_flag_2)
>> 		...
>> 
>> I suppose applying this model here would address Simon's extensibility 
>> concern.
> 
> Yes, that is the model I had in mind.

The only thing is that we actually need to return both 0 and -EOPNOTSUPP 
for unsupported flags. The dynamic flag requires 0 when not supported 
(and supported) AFAICS.
Setting a mask as 'supported' for a feature that is not really supported 
defeats the notion of 'supported' IMHO.