netdev - Re: [PATCH v2] net: mtk_sgmii: implement mtk_pcs

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Date:   Mon, 16 Jan 2023 18:54:05 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Bjørn Mork <bjorn@...k.no>
Cc:     Frank Wunderlich <frank-w@...lic-files.de>,
        Frank Wunderlich <linux@...web.de>,
        linux-mediatek@...ts.infradead.org,
        Alexander Couzens <lynxis@...0.eu>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: mtk_sgmii: implement mtk_pcs_ops

On Mon, Jan 16, 2023 at 07:30:27PM +0100, Bjørn Mork wrote:
> "Russell King (Oracle)" <linux@...linux.org.uk> writes:
> 
> > That all looks fine. However, I'm running out of ideas.
> 
> Thanks a lot for the effort in any case.  It's comforting that even the
> top experts can't figure out this one :-)
> 
> 
> > What we seem to have is:
> >
> > PHY:
> > VSPEC1_SGMII_CTRL = 0x34da
> > VSPEC1_SGMII_STAT = 0x000e
> >
> > The PHY is programmed to exchange SGMII with the host PCS, and it
> > says that it hasn't completed that exchange (bit 5 of STAT).
> >
> > The Mediatek PCS says:
> > BMCR = 0x1140		AN enabled
> > BMSR = 0x0008		AN capable
> > ADVERTISE = 0x0001	SGMII response (bit 14 is clear, hardware is
> > 			supposed to manage that bit)
> > LPA = 0x0000		SGMII received control word (nothing)
> > SGMII_MODE = 0x011b	SGMII mode, duplex AN, 1000M, Full duplex,
> > 			Remote fault disable
> >
> > which all looks like it should work - but it isn't.
> >
> > One last thing I can think of trying at the moment would be writing
> > the VSPEC1_SGMII_CTRL with 0x36da, setting bit 9 which allegedly
> > restarts the SGMII exchange. There's some comments in the PHY driver
> > that this may be needed - maybe it's necessary once the MAC's PCS
> > has been switched to SGMII mode.
> 
> 
> Tried that now.  Didn't change anything.  And still no packets.
> 
> root@...nWrt:/# mdio mdio-bus 6:30 raw 8
> 0x34da
> root@...nWrt:/# mdio mdio-bus 6:30 raw 9
> 0x000e
> root@...nWrt:/# mdio mdio-bus 6:30 raw 8 0x36da
> root@...nWrt:/# mdio mdio-bus 6:30 raw 8
> 0x34da
> root@...nWrt:/# mdio mdio-bus 6:30 raw 9
> 0x000e

If bit 9 is indeed the restart-an bit, it will be self-clearing, so
I wouldn't expect a read back of it to change to 0x36da.

I guess next thing to try is clearing and setting the AN enable bit,
bit 12, so please try this:

mdio mdio-bus 6:30 raw 8 0x24da
mdio mdio-bus 6:30 raw 8 0x36da
mdio mdio-bus 6:30 raw 9

If that doesn't work, then let's try something a bit harder:

mdio mdio-bus 6:30 raw 8 0xb4da
mdio mdio-bus 6:30 raw 9

Please let me know the results from those.

Thanks.

-- 
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