netdev - Re: [RFC PATCH net-next 20/22] net: dsa: mt7530: force link-down on MACs before reset on MT7530

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Date:   Fri, 21 Apr 2023 20:06:18 +0100
From:   Daniel Golle <daniel@...rotopia.org>
To:     Arınç ÜNAL <arinc.unal@...nc9.com>
Cc:     Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Russell King <linux@...linux.org.uk>,
        Richard van Schagen <richard@...terhints.com>,
        Richard van Schagen <vschagen@...com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        erkin.bozoglu@...ont.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [RFC PATCH net-next 20/22] net: dsa: mt7530: force link-down on
 MACs before reset on MT7530

On Fri, Apr 21, 2023 at 09:47:16PM +0300, Arınç ÜNAL wrote:
> On 21.04.2023 21:42, Daniel Golle wrote:
> > On Fri, Apr 21, 2023 at 05:36:46PM +0300, arinc9.unal@...il.com wrote:
> > > From: Arınç ÜNAL <arinc.unal@...nc9.com>
> > > 
> > > Force link-down on all MACs before internal reset. Let's follow suit commit
> > > 728c2af6ad8c ("net: mt7531: ensure all MACs are powered down before
> > > reset").
> > > 
> > > Tested-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> > > Signed-off-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> > > ---
> > >   drivers/net/dsa/mt7530.c | 4 ++++
> > >   1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> > > index ac1e3c58aaac..8ece3d0d820c 100644
> > > --- a/drivers/net/dsa/mt7530.c
> > > +++ b/drivers/net/dsa/mt7530.c
> > > @@ -2203,6 +2203,10 @@ mt7530_setup(struct dsa_switch *ds)
> > >   		return -EINVAL;
> > >   	}
> > > +	/* Force link-down on all MACs before internal reset */
> > > +	for (i = 0; i < MT7530_NUM_PORTS; i++)
> > > +		mt7530_write(priv, MT7530_PMCR_P(i), PMCR_FORCE_LNK);
> > > +
> > 
> > Moving this part to mt753x_setup just before calling priv->info->sw_setup(ds);
> > is probably better. Though it isn't documented I assume that the requirement
> > to have the ports in force-link-down may also apply to MT7988, and for sure
> > it doesn't do any harm.
> > 
> > Hence I suggest to squash this change:
> > diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> > index a2cb7e296165e..998c4e8930cd3 100644
> > --- a/drivers/net/dsa/mt7530.c
> > +++ b/drivers/net/dsa/mt7530.c
> > @@ -2203,10 +2203,6 @@ mt7530_setup(struct dsa_switch *ds)
> >   		return -EINVAL;
> >   	}
> > -	/* Force link-down on all MACs before internal reset */
> > -	for (i = 0; i < MT7530_NUM_PORTS; i++)
> > -		mt7530_write(priv, MT7530_PMCR_P(i), PMCR_FORCE_LNK);
> > -
> >   	/* Reset the switch through internal reset */
> >   	mt7530_write(priv, MT7530_SYS_CTRL,
> >   		     SYS_CTRL_PHY_RST | SYS_CTRL_SW_RST |
> > @@ -2423,10 +2419,6 @@ mt7531_setup(struct dsa_switch *ds)
> >   		dev_info(priv->dev, "found MT7531BE\n");
> >   	}
> > -	/* all MACs must be forced link-down before sw reset */
> > -	for (i = 0; i < MT7530_NUM_PORTS; i++)
> > -		mt7530_write(priv, MT7530_PMCR_P(i), MT7531_FORCE_LNK);
> > -
> >   	/* Reset the switch through internal reset */
> >   	mt7530_write(priv, MT7530_SYS_CTRL,
> >   		     SYS_CTRL_PHY_RST | SYS_CTRL_SW_RST |
> > @@ -2907,6 +2899,10 @@ mt753x_setup(struct dsa_switch *ds)
> >   		priv->pcs[i].port = i;
> >   	}
> > +	/* Force link-down on all MACs before setup */
> > +	for (i = 0; i < MT7530_NUM_PORTS; i++)
> > +		mt7530_write(priv, MT7530_PMCR_P(i), PMCR_FORCE_LNK);
> 
> MT7531 has got a different bit on the register for this, MT7531_FORCE_LNK.
> Are you sure PMCR_FORCE_LNK would work for MT7531 too?

No, I had overlooked that. As the effects of not doing the
force-link-down before the reset are subtle and depend on the
link-partners I may not have cought them in my tests.


> 
> Arınç