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Message-ID: <21ec269340a83f436bbf7a23a2be4289c88b70dd.camel@bootlin.com>
Subject: Re: [PATCH net v3] net: macb: remove change_mtu callback
From: Thomas Perrot <thomas.perrot@bootlin.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>, Claudiu Beznea
 <claudiu.beznea@tuxon.dev>, "David S . Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>,
 netdev@vger.kernel.org,  linux-kernel@vger.kernel.org
Date: Wed, 13 Mar 2024 14:39:05 +0100
In-Reply-To: <20240311161727.629c0bab@kernel.org>
References: <20240311154315.2575297-1-thomas.perrot@bootlin.com>
	 <20240311161727.629c0bab@kernel.org>
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Hello,

On Mon, 2024-03-11 at 16:17 -0700, Jakub Kicinski wrote:
> On Mon, 11 Mar 2024 16:43:15 +0100 thomas.perrot@bootlin.com=C2=A0wrote:
> > Because it doesn't allow MTU changes when the interface is up,
> > although
> > it is not necessary.
> >=20
> > This callback has been added to add in a first implementation of
> > the Jumbo
> > support [1],since it has been reworked and moved to the probe [2].
> >=20
> > With this patch the core will set the MTU, regardless of if the
> > interface
> > is up or not.
> >=20
> > [1] commit a5898ea09aad ("net: macb: Add change_mtu callback with
> > =C2=A0=C2=A0=C2=A0 jumbo support")
> > [2] commit 44770e1180de ("ethernet: use core min/max MTU checking")
> >=20
> > Fixes: 44770e1180de ("ethernet: use core min/max MTU checking")
>=20
> static void macb_init_rx_buffer_size(struct macb *bp, size_t size)
> {
> 	if (!macb_is_gem(bp)) {
> 		bp->rx_buffer_size =3D MACB_RX_BUFFER_SIZE;
> 	} else {
> 		bp->rx_buffer_size =3D size;
>=20
> where size is:
>=20
> 	size_t bufsz =3D dev->mtu + ETH_HLEN + ETH_FCS_LEN +
> NET_IP_ALIGN;
>=20
> I guess you tested this on a platform where !macb_is_gem(bp) ?

Thank you for your review, indeed that won=E2=80=99t be correct on GEM in w=
hen
the MTU used to initialize the RX buffer is lower than the new MTU.

So, I will suggest another patch with an acceptable solution.

Kind regards,
Thomas Perrot

> Otherwise the buffer size seems to be based on MTU and the proposed
> change won't be correct.

--=20
Thomas Perrot, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com


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