netdev - genphy_read_status() vs. 1000bT Pause capability

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Message-ID: <1490662190.3177.91.camel@kernel.crashing.org>
Date:   Tue, 28 Mar 2017 11:49:50 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     netdev@...r.kernel.org
Subject: genphy_read_status() vs. 1000bT Pause capability

Hi !

I noticed that flow control isn't being enabled on a system I'm
working on by default. I've tracked it down to two things:

 - The realtec.c PHY driver doesn't have Pause or Asym_Pause in
its exposed capabilities. This is in part because PHY_GBIT_FEATURES
does not include SUPPORTED_Pause and SUPPORTED_Asym_Pause. Is there
a specific reason for that ?

 - After I've hacked the above, I get in genphy_read_status():

lpa=c1e1 lpagb=3800 adv=de1 common_adv=1e1 common_adv_gb=800

So we have negociated 1000bT full duplex. LPA_PAUSE's aren't set
but I was under the impression that in Gigabit mode, LPA bit 0x80
which *is* set, meant ADVERTISE_1000XPAUSE which is the pause
capability isn't it ? Or am I confusing with something else ?
This seems to be how mii_adv_to_ethtool_adv_x() decodes them
but that function is not called by genphy_read_status()...

Now it's been a while since I hacked network drivers and back then
everybody did their own salad with gigabit PHYs so it's very possible
that I missed something here.

Should we update genphy_read_status() to grab the pause details
from mii_adv_to_ethtool_adv_x() when in 1000bT mode ?

Thanks !

Cheers,
Ben.