netdev - Re: [PATCH net v5 2/2] net: ethernet: cortina: Bypass checksumming engine of alien ethertypes

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Date: Sat, 6 Jan 2024 01:17:36 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Hans Ulli Kroll <ulli.kroll@...glemail.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Household Cang <canghousehold@....com>, Romain Gantois <romain.gantois@...tlin.com>, 
	netdev@...r.kernel.org
Subject: Re: [PATCH net v5 2/2] net: ethernet: cortina: Bypass checksumming
 engine of alien ethertypes

On Thu, Jan 4, 2024 at 1:53 AM Vladimir Oltean <olteanv@...il.com> wrote:

> "Looking at the size of the frame is probably just wrong." yet you keep it.
>
> Not only is this confusing for you to say this, but I believe that the
> skb->len check is the _only_ thing that is needed. Explanation below.

You are right (as usual).

And the analysis you write make perfect sense.

I dropped the entire patch, and send only 1/2 in v6.

> The one difference between DSA and VLAN is that for DSA, you sometimes
> set TSS_BYPASS_BIT (for large frames) and for VLAN you never do.
(...)
> Do you know what "TSS_BYPASS_BIT" does, exactly?

No.

The datasheet very annoyingly omits all details on the TSS
(the checksumming engine), and the documentation of the bits
in "word1" and "word3" only say it is a way to pass configuration
to the checksumming engine. I think it is a genuine oversight
by the document author actually.

Yours,
Linus Walleij