netdev - Re: [PATCH net-next 03/13] net: dsa: sja1105: the 0x1F0000 SGMII "base address" is actually MDIO_MMD

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Message-ID: <20210525091255.yewlypibydfbux6b@skbuf>
Date:   Tue, 25 May 2021 09:12:56 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
CC:     Vladimir Oltean <olteanv@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH net-next 03/13] net: dsa: sja1105: the 0x1F0000 SGMII
 "base address" is actually MDIO_MMD_VEND2

On Mon, May 24, 2021 at 07:19:17PM -0700, Florian Fainelli wrote:
> 
> 
> On 5/24/2021 4:22 PM, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.oltean@....com>
> > 
> > Looking at the SGMII PCS from SJA1110, which is accessed indirectly
> > through a different base address as can be seen in the next patch, it
> > appears odd that the address accessed through indirection still
> > references the base address from the SJA1105S register map (first MDIO
> > register is at 0x1f0000), when it could index the SGMII registers
> > starting from zero.
> > 
> > Except that the 0x1f0000 is not a base address at all, it seems. It is
> > 0x1f << 16 | 0x0000, and 0x1f is coding for the vendor-specific MMD2.
> > So, it turns out, the Synopsys PCS implements all its registers inside
> > the vendor-specific MMDs 1 and 2 (0x1e and 0x1f). This explains why the
> > PCS has no overlaps (for the other MMDs) with other register regions of
> > the switch (because no other MMDs are implemented).
> > 
> > Change the code to remove the SGMII "base address" and explicitly encode
> > the MMD for reads/writes. This will become necessary for SJA1110 support.
> > 
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > ---
> 
> [snip]
> >  
> > @@ -1905,7 +1904,9 @@ int sja1105_static_config_reload(struct sja1105_private *priv,
> >  		mac[i].speed = SJA1105_SPEED_AUTO;
> >  
> >  		if (sja1105_supports_sgmii(priv, i))
> > -			bmcr[i] = sja1105_sgmii_read(priv, i, MII_BMCR);
> > +			bmcr[i] = sja1105_sgmii_read(priv, i,
> > +						     MDIO_MMD_VEND2,
> > +						     MDIO_CTRL1);
> 
> This appears different from what you had before?

MDIO_CTRL1 is the clause 45 alias of MII_BMCR, all in all it is still a
cosmetic change in line with the patch's idea of expressing accesses as
clause 45. I didn't replace the "bmcr" variable names because that would
have introduced more noise than I would have liked.