netdev - Re: [PATCH net-next 1/2] net: phy: aquantia: add rate

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Date:   Tue, 28 Jan 2020 17:55:01 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ykaukab@...e.de" <ykaukab@...e.de>
Subject: Re: [PATCH net-next 1/2] net: phy: aquantia: add rate_adaptation indication

Hi Florian,

On Mon, 27 Jan 2020 at 19:44, Florian Fainelli <f.fainelli@...il.com> wrote:
>
> On 1/22/20 11:38 PM, Madalin Bucur (OSS) wrote:
> >> -----Original Message-----
> >> From: Florian Fainelli <f.fainelli@...il.com>
> >> Sent: Wednesday, January 22, 2020 7:58 PM
> >> To: Madalin Bucur (OSS) <madalin.bucur@....nxp.com>; davem@...emloft.net
> >> Cc: andrew@...n.ch; hkallweit1@...il.com; netdev@...r.kernel.org;
> >> ykaukab@...e.de
> >> Subject: Re: [PATCH net-next 1/2] net: phy: aquantia: add rate_adaptation
> >> indication
> >>
> >> On 1/22/20 5:59 AM, Madalin Bucur wrote:
> >>> The AQR PHYs are able to perform rate adaptation between
> >>> the system interface and the line interfaces. When such
> >>> a PHY is deployed, the ethernet driver should not limit
> >>> the modes supported or advertised by the PHY. This patch
> >>> introduces the bit that allows checking for this feature
> >>> in the phy_device structure and its use for the Aquantia
> >>> PHYs.
> >>>
> >>> Signed-off-by: Madalin Bucur <madalin.bucur@....nxp.com>
> >>> ---
> >>>  drivers/net/phy/aquantia_main.c | 3 +++
> >>>  include/linux/phy.h             | 3 +++
> >>>  2 files changed, 6 insertions(+)
> >>>
> >>> diff --git a/drivers/net/phy/aquantia_main.c
> >> b/drivers/net/phy/aquantia_main.c
> >>> index 975789d9349d..36fdd523b758 100644
> >>> --- a/drivers/net/phy/aquantia_main.c
> >>> +++ b/drivers/net/phy/aquantia_main.c
> >>> @@ -209,6 +209,9 @@ static int aqr_config_aneg(struct phy_device
> >> *phydev)
> >>>     u16 reg;
> >>>     int ret;
> >>>
> >>> +   /* add here as this is called for all devices */
> >>> +   phydev->rate_adaptation = 1;
> >>
> >> How about introducing a new PHY_SUPPORTS_RATE_ADAPTATION flag and you
> >> set that directly from the phy_driver entry? using the "flags" bitmask
> >> instead of adding another structure member to phy_device?
> >
> > I've looked at the phydev->dev_flags use, it seemed to me that mostly it
> > is used to convey configuration options towards the PHY.
>
> You read me incorrectly, I am suggesting using the phy_driver::flags
> member, not the phy_device::dev_flags entry, please re-consider your
> position.
>

Whether the PHY performs rate adaptation is a dynamic property.
It will perform it at wire speeds lower than 2500Mbps (1000/100) when
system side is 2500Base-X, but not at wire speed 2500 & 2500Base-X,
and not at wire speed 1000 & USXGMII.
You can't really encode that in phydev->flags.

I was actually searching for a way to encode some more PHY capabilities:
- Does it work with in-band autoneg enabled?
- Does it work with in-band autoneg bypassed?
- Does it emit pause frames? <- Madalin got ahead of me on this one.

For the first 2, I want a mechanism for the PHY library to figure out
whether the MAC and the PHY should use in-band autoneg or not. If both
support in-band autoneg, that would be preferred. Otherwise,
out-of-band (MDIO) is preferred, and in-band autoneg is explicitly
disabled in both, if that is claimed to be supported. Otherwise,
report error to user. Yes, this deprecates "managed =
'in-band-status'" in the device tree, and that's for (what I think is)
the better. We can make "managed = 'in-band-status'" to just clear the
MAC's ability to support the "in-band autoneg bypassed" mode.

So I thought a function pointer in the phy driver would be better, and
more extensible.
Thoughts?

> --
> Florian

Regards,
-Vladimir