[PATCH v7 7/8] net: add MV88E6xxx DSA driver

[Vladimir Oltean]

On Wed, Oct 26, 2022 at 01:59:19PM -0700, Tim Harvey wrote:
> not sure honestly - it's in the original drivers/net/phy/mv88e61xxx.c
> driver that I based this one off of.

You keep saying this; it doesn't matter where it comes from, the point
is whether it's useful to keep it in a new driver or not...

> From the functional spec of the 88E6176:
> - energy detect mode1 (what I'm doing here):
> only the signal detection circuitry and the serial management
> interface are active. If the PHY detects energy on the line, it starts
> to Auto-Negotiate sending FLPs for 5 seconds. If at the end of 5
> seconds the Auto-Negotiation is not completed, then the PHY stops
> sending FLPs and goes back to monitoring receive energy. If
> Auto-Negotation is completed, then the PHY goes into normal
> 10/100/1000 MBps operation. If during normal operation the link is
> lost, the PHY will re-start Auto-Negotiation. If no energy is detected
> after 5 seconds, the PHY goes back to monitoring receive energy.
> - energy detect mode2 (appears to be the power-on default):
> The PHY sends out a single 10Mbps NLP (Normal Link Pulse) every on
> second. Except for this difference, Mode 2 is identical to Mode 1
> operation. If the device is in Mode 1, it cannot wake up a connected
> device; therefore, the connected device must be transmitting NLPs, or
> either device must be woken up through register access. If the device
> is in Mode 2, then it can wake a connected device.
> - energy detect disabled:
> Normal 10/100/1000 mbps operation
> 
> You bring up a great point regarding the Marvell PHY driver not doing
> this... I'm happy to kill it off?

Ah, ok, it's a low power mode.

That being said, it seems like Marvell is saying: hey, we offer you the
ability to save power (when the PHY should be up) by disabling much of
the PHY circuitry, just leave on some signal detection circuit.
We certainly won't be emitting any NLP such that the link partner will
know the link is up. You go first and then we'll respond!

I wonder what happens if you connect 2 Marvell PHY ports with Energy
Detect to each other... the link shouldn't come up, right?

I absolutely think that this setting has no purpose in a bootloader driver.
Just a potential pain point. You want the bootloader networking to be
bullet proof.

Kill it!