netdev - Re: [PATCH v2 11/11] net: dsa: mt7530: use external PCS driver

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Date:   Fri, 10 Feb 2023 22:17:15 +0000
From:   Daniel Golle <daniel@...rotopia.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        John Crispin <john@...ozen.org>, Felix Fietkau <nbd@....name>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        DENG Qingfang <dqfext@...il.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Vladimir Oltean <olteanv@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Jianhui Zhao <zhaojh329@...il.com>,
        Bjørn Mork <bjorn@...k.no>
Subject: Re: [PATCH v2 11/11] net: dsa: mt7530: use external PCS driver

On Fri, Feb 10, 2023 at 10:56:57AM +0000, Russell King (Oracle) wrote:
> On Tue, Feb 07, 2023 at 02:24:17PM +0000, Daniel Golle wrote:
> > @@ -2728,11 +2612,11 @@ mt753x_phylink_mac_select_pcs(struct dsa_switch *ds, int port,
> >  
> >  	switch (interface) {
> >  	case PHY_INTERFACE_MODE_TRGMII:
> > +		return &priv->pcs[port].pcs;
> >  	case PHY_INTERFACE_MODE_SGMII:
> >  	case PHY_INTERFACE_MODE_1000BASEX:
> >  	case PHY_INTERFACE_MODE_2500BASEX:
> > -		return &priv->pcs[port].pcs;
> > -
> > +		return priv->ports[port].sgmii_pcs;
> 
> My only concern here is that we also use the PCS when in TRGMII mode in
> this driver, but the mtk pcs code from mtk_eth_soc doesn't handle
> TRGMII (and getting the link timer will fail for this mode, causing
> the pcs_config() method to fail.)
> 
> Thus, this driver will stop working in TRGMII mode.

I've just built and tested this on MT7623 BPi-R2 board with MT7530
connnected to SoC via TRGMII and observed that it all works fine.

However, on this platform we could safe some bytes by still allowing
mt7530.c to be built without pcs-mtk-lynxi which isn't used on MT7623
by either the ethernet or the switch driver.

To me this is not a priority, and doing that would involve adding some
ifdef'ery which isn't really nice. However, if anyone has a strong
opinion in favor of allowing mt7530.c (or even mtk_eth_soc) to be built
without pcs-mtk-lynxi, let me know and I will make the necessary
changes.