netdev - Re: [PATCH net 2/2] net: phylink: use USXGMII control-word format to parse Q-USGMII word

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Date: Thu, 8 Jun 2023 19:53:30 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com, Andrew Lunn
 <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>, Heiner Kallweit
 <hkallweit1@...il.com>, linux-arm-kernel@...ts.infradead.org,
 Horatiu.Vultur@...rochip.com, Allan.Nielsen@...rochip.com,
 UNGLinuxDriver@...rochip.com, Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net 2/2] net: phylink: use USXGMII control-word format
 to parse Q-USGMII word

Hi Russell,

On Thu, 8 Jun 2023 17:32:52 +0100
"Russell King (Oracle)" <linux@...linux.org.uk> wrote:

> On Thu, Jun 08, 2023 at 06:34:15PM +0200, Maxime Chevallier wrote:
> > diff --git a/include/uapi/linux/mdio.h b/include/uapi/linux/mdio.h
> > index 256b463e47a6..1d20a9082507 100644
> > --- a/include/uapi/linux/mdio.h
> > +++ b/include/uapi/linux/mdio.h
> > @@ -444,4 +444,7 @@ static inline __u16 mdio_phy_id_c45(int prtad, int devad)
> >  #define MDIO_USXGMII_5000FULL		0x1a00	/* 5000Mbps full-duplex */
> >  #define MDIO_USXGMII_LINK		0x8000	/* PHY link with copper-side partner */
> >  
> > +/* Usgmii control word is based on Usxgmii, masking away 2.5, 5 and 10Gbps */
> > +#define MDIO_USGMII_SPD_MASK		0x0600  
> 
> This isn't correct:
> 
> 11:9	Speed: Bit 11, 10, 9:
> 	1 1 1 to 011 = Reserved
> 	0 1 0 = 1000 Mbps: 1000BASE-TX, 1000BASE-X
> 	0 0 1 = 100 Mbps: 100BASE-TX, 100BASE-FX
> 	0 0 0 = 10 Mbps: 10BASET, 10BASE2, 10BASE5
> 
> If we only look at bits 10 and 9, then we're interpreting the reserved
> combinations as valid as well.

That's why I rewrote the decoding helper instead of simply masking away
the extra bit, so that we exclude the 0 1 1 combination ( 10G speed ).

The comment is wrong though.

This patch set needs more coffee,

Best regards,

Maxime