Re: [PATCH] net: phylink: Pass state to pcs_config

On Tue, Dec 14, 2021 at 07:16:53PM -0500, Sean Anderson wrote:

Ok, so let me clarify my understanding. Perhaps this can be eliminated
through a different approach.

When I read the datasheet for mvneta (which hopefully has the same
logic here, since I could not find a datasheet for an mvpp2 device), I
noticed that the Pause_Adv bit said

quoted

It is valid only if flow control mode is defined by Auto-Negotiation
(as defined by the <AnFcEn> bit).

Which I interpreted to mean that if AnFcEn was clear, then no flow
control was advertised. But perhaps it instead means that the logic is
something like

if (AnFcEn)
	Config_Reg.PAUSE = Pause_Adv;
else
	Config_Reg.PAUSE = SetFcEn;

which would mean that we can just clear AnFcEn in link_up if the
autonegotiated pause settings are different from the configured pause
settings.

Having actually played with this hardware quite a bit and observed what
it sends, what it implements for advertising is:

	Config_Reg.PAUSE = Pause_Adv;

Config_Reg gets sent over the 1000BASE-X link to the link partner, and
we receive Remote_Reg from the link partner.

Then, the hardware implements:

	if (AnFcEn)
		MAC_PAUSE = Config_Reg.PAUSE & Remote_Reg.PAUSE;
	else
		MAC_PAUSE = SetFcEn;

In otherwords, AnFcEn controls whether the result of autonegotiation
or the value of SetFcEn controls whether the MAC enables symmetric
pause mode.

Pause_Adv comes from the advertisement, and this is controlled from
ethtool -s and somewhat by ethtool -A.

AnFcEn is controlled purely and only by ethtool -A ... autoneg on|off.
You can't derive this from "state".

SetFcEn comes from ethtool -A ... tx and rx parameters (which must
both be on or both be off.)

Since we have no knowledge what Remote_Reg contains (it's not made
accessible by the hardware), it's impossible to derive whether the
autonegotiated pause settings are different from the configured pause
settings.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel