netdev - Re: [PATCH net-next v3] net: phy: broadcom: add 1000Base-X support for BCM54616S

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Message-ID: <f8de2514-081a-0e6e-fbe2-bcafcd459646@gmail.com>
Date:   Sun, 4 Aug 2019 18:06:58 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>
Cc:     Tao Ren <taoren@...com>, Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Arun Parameswaran <arun.parameswaran@...adcom.com>,
        Justin Chen <justinpopo6@...il.com>,
        netdev <netdev@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>
Subject: Re: [PATCH net-next v3] net: phy: broadcom: add 1000Base-X support
 for BCM54616S

On 04.08.2019 17:59, Vladimir Oltean wrote:
> On Sun, 4 Aug 2019 at 17:52, Andrew Lunn <andrew@...n.ch> wrote:
>>
>>>> The patchset looks better now. But is it ok, I wonder, to keep
>>>> PHY_BCM_FLAGS_MODE_1000BX in phydev->dev_flags, considering that
>>>> phy_attach_direct is overwriting it?
>>>
>>
>>> I checked ftgmac100 driver (used on my machine) and it calls
>>> phy_connect_direct which passes phydev->dev_flags when calling
>>> phy_attach_direct: that explains why the flag is not cleared in my
>>> case.
>>
>> Yes, that is the way it is intended to be used. The MAC driver can
>> pass flags to the PHY. It is a fragile API, since the MAC needs to
>> know what PHY is being used, since the flags are driver specific.
>>
>> One option would be to modify the assignment in phy_attach_direct() to
>> OR in the flags passed to it with flags which are already in
>> phydev->dev_flags.
>>
>>         Andrew
> 
> Even if that were the case (patching phy_attach_direct to apply a
> logical-or to dev_flags), it sounds fishy to me that the genphy code
> is unable to determine that this PHY is running in 1000Base-X mode.
> 
> In my opinion it all boils down to this warning:
> 
> "PHY advertising (0,00000200,000062c0) more modes than genphy
> supports, some modes not advertised".
> 
The genphy code deals with Clause 22 + Gigabit BaseT only.
Question is whether you want aneg at all in 1000Base-X mode and
what you want the config_aneg callback to do.
There may be some inspiration in the Marvel PHY drivers.

> You see, the 0x200 in the above advertising mask corresponds exactly
> to this definition from ethtool.h:
>     ETHTOOL_LINK_MODE_1000baseX_Full_BIT    = 41,
> 
> But it gets truncated and hence lost.
> 
> Regards,
> -Vladimir
> 
Heiner