[PATCH RFC net-next 1/5] net: dsa: mt7530: Convert to PHYLINK API

Daniel Santos daniel.santos at pobox.com
Fri Jun 28 00:16:45 PDT 2019

Hello Andrew,

On 6/27/19 2:28 PM, Andrew Lunn wrote:
>>> Looking at the data sheet page, you want FORCE_MODE_Pn set. You never
>>> want the MAC directly talking to the PHY. Bad things will happen.
>> So what exactly do you mean by the MAC directly talking to the PHY?  Do
>> you mean setting speed, duplex, etc. via the MAC registers instead of
>> via MDIO to the MII registers of the PHY?
> The data sheet implies the MAC hardware performs reads on the PHY to
> get the status, and then uses that to configure the MAC. This is often
> called PHY polling. The MAC hardware however has no idea what the PHY
> driver is doing. The MAC does not take the PHY mutex. So the PHY
> driver might be doing something at the same time the MAC hardware
> polls the PHY, and it gets odd results. Some PHYs have multiple pages,
> and for example reading the temperature sensor means swapping
> pages. If the MAC hardware was to poll while the sensor is being read,
> it would not get the link status, it would read some random
> temperature register.
> So you want the PHY driver to read the results of auto-neg and it then
> tell the MAC the results, so the MAC can be configured correctly.

Thank you, this is very helpful!  I finally understand why these
settings are in two different places. :)  Unfortunately this driver (in
OpenWRT) does a lot of "magic" during init to registers that I don't
have documentation for, but I see where auto-polling can be disabled now.

>>> Then use FORCE_RX_FC_Pn and FORCE_TX_Pn to reflect phydev->pause and
>>> phydev->asym_pause.
>>> The same idea applies when using phylink.
>>>     Andrew
>> You're help is greatly appreciated here.  Admittedly, I'm also trying to
>> get this working in the now deprecated swconfig for a 3.18 kernel that's
>> in production.
> I'm not very familiar with swconfig. Is there software driving the
> PHY? If not, it is then safe for the MAC hardware to poll the PHY.
>      Andrew

swconfig is an netlink-based interface the OpenWRT team developed for
configuring switches before DSA was converted into a vendor-neutral
interface.  Now that DSA does what swconfig was designed for it has been
deprecated, although (to my knowledge) we don't yet have DSA for all
devices that OpenWRT supports.


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