netdev - Re: [PATCH net-next v3 1/7] bnxt_en: add support for rx-copybreak ethtool command

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Message-ID: <20241008111058.6477e60c@kernel.org>
Date: Tue, 8 Oct 2024 11:10:58 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Taehee Yoo <ap420073@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Michael Chan <michael.chan@...adcom.com>,
 davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.com,
 almasrymina@...gle.com, netdev@...r.kernel.org, linux-doc@...r.kernel.org,
 donald.hunter@...il.com, corbet@....net, kory.maincent@...tlin.com,
 maxime.chevallier@...tlin.com, danieller@...dia.com,
 hengqi@...ux.alibaba.com, ecree.xilinx@...il.com,
 przemyslaw.kitszel@...el.com, hkallweit1@...il.com, ahmed.zaki@...el.com,
 paul.greenwalt@...el.com, rrameshbabu@...dia.com, idosch@...dia.com,
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 aleksander.lobakin@...el.com, dw@...idwei.uk, sridhar.samudrala@...el.com,
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Subject: Re: [PATCH net-next v3 1/7] bnxt_en: add support for rx-copybreak
 ethtool command

On Sat, 5 Oct 2024 15:29:54 +0900 Taehee Yoo wrote:
> > > I think a single value of 0 that means disable RX copybreak is more
> > > clear and intuitive.  Also, I think we can allow 64 to be a valid
> > > value.
> > >
> > > So, 0 means to disable.  1 to 63 are -EINVAL and 64 to 1024 are valid.  Thanks.  
> >
> > Please spend a little time and see what other drivers do. Ideally we
> > want one consistent behaviour for all drivers that allow copybreak to
> > be disabled.  
> 
> There is no specific disable value in other drivers.
> But some other drivers have min/max rx-copybreak value.
> If rx-copybreak is low enough, it will not be worked.
> So, min value has been working as a disable value actually.
> 
> I think Andrew's point makes sense.
> So I would like to change min value from 65 to 64, not add a disable value.

Where does the min value of 64 come from? Ethernet min frame length?

IIUC the copybreak threshold is purely a SW feature, after this series.
If someone sets the copybreak value to, say 13 it will simply never
engage but it's not really an invalid setting, IMHO. Similarly setting
it to 0 makes intuitive sense (that's how e1000e works, AFAICT).