netdev - Re: [PATCH net] net: dsa: mv88e6xxx: Disable AN on 2500base-x for Amethyst

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Message-ID: <20211125184551.2530cc95@thinkpad>
Date:   Thu, 25 Nov 2021 18:45:51 +0100
From:   Marek Behún <kabel@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, Russell King <rmk+kernel@...linux.org.uk>,
        Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Subject: Re: [PATCH net] net: dsa: mv88e6xxx: Disable AN on 2500base-x for
 Amethyst

On Thu, 25 Nov 2021 16:37:40 +0100
Andrew Lunn <andrew@...n.ch> wrote:

> On Thu, Nov 25, 2021 at 03:43:59PM +0100, Marek Behún wrote:
> > Amethyst does not support autonegotiation in 2500base-x mode.  
> 
> Hi Marek
> 
> I tried to avoid using Marvells internal names for these devices. I
> don't think these names exist in the datasheet? They are visible in
> the SDK, but that is not so widely available. So if you do want to use
> these names, please also reference the name we use in the kernel,
> mv88e6393x.

I used these names in previous commit that are already merged (search
for Amethyst, Topaz, Peridot). But if you want, I can send v2. Please
let me know if I should send v2.

> > It does not link with AN enabled with other devices.
> > Disable autonegotiation for Amethyst in 2500base-x mode.
> > 
> > +int mv88e6393x_serdes_pcs_config(struct mv88e6xxx_chip *chip, int port,
> > +				 int lane, unsigned int mode,
> > +				 phy_interface_t interface,
> > +				 const unsigned long *advertise)
> > +{
> > +	if (interface == PHY_INTERFACE_MODE_2500BASEX)
> > +		return 0;
> > +
> > +	return mv88e6390_serdes_pcs_config(chip, port, lane, mode, interface,
> > +					   advertise);
> > +}  
> 
> What happens when changing from say 1000BaseX to 2500BaseX? Do you
> need to disable the advertisement which 1000BaseX might of enabled?
> 
>      Andrew

I don't need to disable it, it is disabled on it's own by cmode change.

Moreover I did some experiments on 88E6393X vs 88E6190.

It is a little weird for 6393x.

On 6190
- resetting the SerDes (BMCR_RESET) does not have impact on the
  BMCR_ANENABLE bit, but changing cmode does

  when cmode is changed to SGMII or 1000base-x, it is enabled, for
  2500base-x it is disabled

- resetting the SerDes (BMCR_RESET) when cmode is
  - sgmii, changes value of the MV88E6390_SGMII_ADVERTISE to 0x0001
    automatically
  - 1000base-x or 2500base-x does not change the value of adv register

  moreover it seems that changing cmode also resets the the SerDes

On 6393x:
- the BMCR behaves the same as in 6190: the switch defaults to AN
  disabled for 2500base-x, and enabled for 1000base-x and SGMII

- the difference is that there are weird values written to
  MV88E6390_SGMII_ADVERTISE on SerDes reset (which is done by switch
  when changing cmode)

  for 1000base-x, the value is 0x9120
  for 2500base-x, the value is 0x9f41

  I don't understand why they changed it so for 6393x.

Marek