netdev - Re: [PATCH 1/2] net: dsa: ksz: pad frame to 64 bytes for transmission

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Date:   Sun, 29 Nov 2020 20:48:25 +0100
From:   Jean Pihet <jean.pihet@...oldbits.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Ryan Barnett <ryan.barnett@...kwellcollins.com>,
        Conrad Ratschan <conrad.ratschan@...kwellcollins.com>,
        Hugo Cornelis <hugo.cornelis@...ensium.com>,
        Arnout Vandecappelle <arnout.vandecappelle@...ensium.com>
Subject: Re: [PATCH 1/2] net: dsa: ksz: pad frame to 64 bytes for transmission

Andrew,

On Sun, Nov 29, 2020 at 8:38 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Sun, Nov 29, 2020 at 08:34:27PM +0100, Jean Pihet wrote:
> > Hi Andrew,
> >
> > On Sun, Nov 29, 2020 at 5:56 PM Andrew Lunn <andrew@...n.ch> wrote:
> > >
> > > On Sun, Nov 29, 2020 at 11:23:59AM +0100, Jean Pihet wrote:
> > > > Some ethernet controllers (e.g. TI CPSW) pad the frames to a minimum
> > > > of 64 bytes before the FCS is appended. This causes an issue with the
> > > > KSZ tail tag which could not be the last byte before the FCS.
> > > > Solve this by padding the frame to 64 bytes minus the tail tag size,
> > > > before the tail tag is added and the frame is passed for transmission.
> > >
> > > Hi Jean
> > >
> > > what tree is this based on? Have you seen
> > The patches are based on the latest mainline v5.10-rc5. Is this the
> > recommended version to submit new patches?
>
> No, that is old. Please take a read of:
>
> https://www.kernel.org/doc/html/latest/networking/netdev-FAQ.html

Ok got it, thx!

Found the commit 88fda8ee and its parent [1] with the following
comment, which seems to indicate that my patch is not needed anymore.
Can you confirm?

/* For tail taggers, we need to pad short frames ourselves, to ensure
+ * that the tail tag does not fail at its role of being at the end of
+ * the packet, once the master interface pads the frame. Account for
+ * that pad length here, and pad later.
...

[1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=a3b0b6479700a5b0af2c631cb2ec0fb7a0d978f2

Thx,
Jean

>
>         Andrew