netdev - Re: [RFC PATCH net-next] net: ethernet: mediatek: support setting MTU

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Date:   Fri, 30 Oct 2020 13:36:48 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     netdev <netdev@...r.kernel.org>, Felix Fietkau <nbd@....name>,
        John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Landen Chao <landen.chao@...iatek.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        René van Dorst <opensource@...rst.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Frank Wunderlich <frank-w@...lic-files.de>
Subject: Re: [RFC PATCH net-next] net: ethernet: mediatek: support setting MTU

On Fri, Oct 30, 2020 at 10:43:51AM +0800, DENG Qingfang wrote:
> On Thu, Oct 29, 2020 at 9:02 PM Andrew Lunn <andrew@...n.ch> wrote:
> >
> > On Thu, Oct 29, 2020 at 02:39:15PM +0800, DENG Qingfang wrote:
> > > MT762x HW supports frame length up to 2048 (maximum length on GDM),
> > > so allow setting MTU up to 2030.
> > >
> > > Signed-off-by: DENG Qingfang <dqfext@...il.com>
> > > ---
> > >
> > > I only tested this on MT7621, no sure if it is applicable for other SoCs
> > > especially MT7628, which has an old IP.
> > >
> > > ---
> > >  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 31 ++++++++++++++++++++-
> > >  drivers/net/ethernet/mediatek/mtk_eth_soc.h | 11 ++++++--
> > >  2 files changed, 38 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> > > index 6d2d60675ffd..a0c56d9be1d5 100644
> > > --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> > > +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> > > @@ -353,7 +353,7 @@ static void mtk_mac_config(struct phylink_config *config, unsigned int mode,
> > >       /* Setup gmac */
> > >       mcr_cur = mtk_r32(mac->hw, MTK_MAC_MCR(mac->id));
> > >       mcr_new = mcr_cur;
> > > -     mcr_new |= MAC_MCR_MAX_RX_1536 | MAC_MCR_IPG_CFG | MAC_MCR_FORCE_MODE |
> > > +     mcr_new |= MAC_MCR_IPG_CFG | MAC_MCR_FORCE_MODE |
> > >                  MAC_MCR_BACKOFF_EN | MAC_MCR_BACKPR_EN | MAC_MCR_FORCE_LINK;
> >
> > Since you no longer set MAC_MCR_MAX_RX_1536, what does the hardware
> > default to?
> 
> 2'b00, i.e. 1518 bytes.

O.K, that fits the default for a netdev.

> It is handled in net_device->max_mtu:
> > eth->netdev[id]->max_mtu = MTK_MAX_RX_LENGTH - MTK_RX_ETH_HLEN;

Cool.

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew