From:   Haiyang Zhang <haiyangz@microsoft.com>
To:     Leon Romanovsky <leon@kernel.org>
CC:     "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Paul Rosswurm <paulros@microsoft.com>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        Long Li <longli@microsoft.com>,
        "ssengar@linux.microsoft.com" <ssengar@linux.microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH net-next] net: mana: Add support for jumbo frame
Thread-Topic: [PATCH net-next] net: mana: Add support for jumbo frame
Thread-Index: AQHZWqm9UOpmxqzZvUOZ7L83A2HDza8DSZcAgAB+W6A=
Date:   Mon, 20 Mar 2023 15:14:32 +0000
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References: <1679261264-26375-1-git-send-email-haiyangz@microsoft.com>
 <20230320074202.GH36557@unreal>
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> -----Original Message-----
> From: Leon Romanovsky <leon@kernel.org>
> Sent: Monday, March 20, 2023 3:42 AM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: linux-hyperv@vger.kernel.org; netdev@vger.kernel.org; Dexuan Cui
> <decui@microsoft.com>; KY Srinivasan <kys@microsoft.com>; Paul Rosswurm
> <paulros@microsoft.com>; olaf@aepfle.de; vkuznets@redhat.com;
> davem@davemloft.net; wei.liu@kernel.org; edumazet@google.com;
> kuba@kernel.org; pabeni@redhat.com; Long Li <longli@microsoft.com>;
> ssengar@linux.microsoft.com; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH net-next] net: mana: Add support for jumbo frame
>=20
> On Sun, Mar 19, 2023 at 02:27:44PM -0700, Haiyang Zhang wrote:
> > During probe, get the hardware allowed max MTU by querying the device
> > configuration. Users can select MTU up to the device limit. Also,
> > when XDP is in use, we currently limit the buffer size to one page.
> >
> > Updated RX data path to allocate and use RX queue DMA buffers with
> > proper size based on the MTU setting.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> > ---
> >  .../net/ethernet/microsoft/mana/mana_bpf.c    |  22 +-
> >  drivers/net/ethernet/microsoft/mana/mana_en.c | 229 ++++++++++++----
> --
> >  include/net/mana/gdma.h                       |   4 +
> >  include/net/mana/mana.h                       |  18 +-
> >  4 files changed, 183 insertions(+), 90 deletions(-)
>=20
> <...>
>=20
> > +static int mana_change_mtu(struct net_device *ndev, int new_mtu)
> > +{
> > +	unsigned int old_mtu =3D ndev->mtu;
> > +	int err, err2;
> > +
> > +	err =3D mana_detach(ndev, false);
> > +	if (err) {
> > +		netdev_err(ndev, "mana_detach failed: %d\n", err);
> > +		return err;
> > +	}
> > +
> > +	ndev->mtu =3D new_mtu;
> > +
> > +	err =3D mana_attach(ndev);
> > +	if (!err)
> > +		return 0;
> > +
> > +	netdev_err(ndev, "mana_attach failed: %d\n", err);
> > +
> > +	/* Try to roll it back to the old configuration. */
> > +	ndev->mtu =3D old_mtu;
> > +	err2 =3D mana_attach(ndev);
>=20
> I second to Francois and agree with him that it is very questionable.
> If mana_attach() failed for first try, you should bail out and not
> retry with some hope that it will pass.
>=20

Will consider. Thanks.