Aw: Re: Re: Re: Re: Re: [PATCH v2] net: mtk_sgmii: implement mtk_pcs_ops

[Frank Wunderlich]

> Gesendet: Samstag, 22. Oktober 2022 um 21:18 Uhr
> Von: "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx>
> An: "Frank Wunderlich" <frank-w@xxxxxxxxxxxxxxx>
> Cc: "Frank Wunderlich" <linux@xxxxxxxxx>, linux-mediatek@xxxxxxxxxxxxxxxxxxx, "Alexander Couzens" <lynxis@xxxxxxx>, "Felix Fietkau" <nbd@xxxxxxxx>, "John Crispin" <john@xxxxxxxxxxx>, "Sean Wang" <sean.wang@xxxxxxxxxxxx>, "Mark Lee" <Mark-MC.Lee@xxxxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, "Eric Dumazet" <edumazet@xxxxxxxxxx>, "Jakub Kicinski" <kuba@xxxxxxxxxx>, "Paolo Abeni" <pabeni@xxxxxxxxxx>, "Matthias Brugger" <matthias.bgg@xxxxxxxxx>, netdev@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> Betreff: Re: Re: Re: Re: Re: [PATCH v2] net: mtk_sgmii: implement mtk_pcs_ops
>
> Hi,
>
> On Sat, Oct 22, 2022 at 07:53:16PM +0200, Frank Wunderlich wrote:
> > > Gesendet: Samstag, 22. Oktober 2022 um 19:05 Uhr
> > > Von: "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx>
> > > On Sat, Oct 22, 2022 at 12:52:00PM +0200, Frank Wunderlich wrote:
> > > > > Gesendet: Samstag, 22. Oktober 2022 um 11:11 Uhr
> > > > > Von: "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx>
> >
> > > > this patch breaks connectivity at least on the sfp-port (eth1).
> >
> > > > pcs_get_state
> > > > [   65.522936] offset:0 0x2c1140
> > > > [   65.522950] offset:4 0x4d544950
> > > > [   65.525914] offset:8 0x40e041a0
> > > > [  177.346183] offset:0 0x2c1140
> > > > [  177.346202] offset:4 0x4d544950
> > > > [  177.349168] offset:8 0x40e041a0
> > > > [  177.352477] offset:0 0x2c1140
> > > > [  177.356952] offset:4 0x4d544950
> > >
> > > Hi,
> > >
> > > Thanks. Well, the results suggest that the register at offset 8 is
> > > indeed the advertisement and link-partner advertisement register. So
> > > we have a bit of progress and a little more understanding of this
> > > hardware.
> > >
> > > Do you know if your link partner also thinks the link is up?
> >
> > yes link is up on my switch, cannot enable autoneg for fibre-port, so port is fixed to 1000M/full flowcontrol enabled.
> >
> > > What I notice is:
> > >
> > > mtk_soc_eth 15100000.ethernet eth1: Link is Up - 1Gbps/Unknown - flow control off
> > >
> > > The duplex is "unknown" which means you're not filling in the
> > > state->duplex field in your pcs_get_state() function. Given the
> > > link parter adverisement is 0x00e0, this means the link partner
> > > supports PAUSE, 1000base-X/Half and 1000base-X/Full. The resolution
> > > is therefore full duplex, so can we hack that in to your
> > > pcs_get_state() so we're getting that right for this testing please?
> >
> > 0xe0 is bits 5-7 are set (in lower byte from upper word)..which one is for duplex?
> >
> > so i should set state->duplex/pause based on this value (maybe compare with own caps)?
> >
> > found a documentation where 5=full,6=half, and bits 7+8 are for pause (symetric/asymetric)
> >
> > regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1+8, &val);
> > partner_advertising = (val & 0x00ff0000) >> 16;
>
> Not quite :) When we have the link partner's advertisement and the BMSR,
> we have a helper function in phylink to do all the gritty work:
>
> 	regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1, &bm);
> 	regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1 + 8, &adv);
>
> 	phylink_mii_c22_pcs_decode_state(state, bm >> 16, adv >> 16);
>
> will do all the work for you without having to care about whether
> you're operating at 2500base-X, 1000base-X or SGMII mode.
>
> > > Now, I'm wondering what SGMII_IF_MODE_BIT0 and SGMII_IF_MODE_BIT5 do
> > > in the SGMSYS_SGMII_MODE register. Does one of these bits set the
> > > format for the 16-bit control word that's used to convey the
> > > advertisements. I think the next step would be to play around with
> > > these and see what effect setting or clearing these bits has -
> > > please can you give that a go?
> >
> > these is not clear to me...should i blindly set these and how to
> > verify what they do?
>
> Yes please - I don't think anyone knows what they do.

i guess BIT0 is the SGMII_EN flag like in other sgmii implementations.
Bit5 is "reserved" in all docs i've found....maybe it is related to HSGMII
or for 1G vs. 2G5.

but how to check what has changed...i guess only the register itself changed
and i have to readout another to check whats changed.

do we really need these 2 bits? reading/setting duplex/pause from/to the register
makes sense, but digging into undocumented bits is much work and we still only guess.

so i would first want to get sgmii working again and then strip the pause/duplex from it.

> > is network broken because of wrong duplex/pause setting? do not
> > fully understand your Patch.
>
> I suspect not having the duplex correct _could_ break stuff, but I
> also wonder whether the PCS is trying to decode the advertisements
> itself and coming out with the wrong settings.
>
> If it's interpreting a link partner advertisement of 0x00e0 using
> SGMII rules, then it will be looking at bits 11 and 10 for the
> speed, both of which are zero, which means 10Mbps - and 1000base-X
> doesn't operate at 10Mbps!

so maybe this breaks sgmii? have you changed this behaviour with your Patch?

> So my hunch is that one of those two IF_MODE_BIT{0,5} _might_ change
> the way the PCS interprets the control word, but as we don't have
> any documentation to go on, only experimentation will answer this
> question.
>
> If these registers are MMIO, you could ensure that you have /dev/mem
> access enabled, and use devmem2 to poke at this register which would
> probably be quicker than doing a build-boot-test cycle with the
> kernel - this is how I do a lot of this kind of discovery when
> documentation is lacking.
>
> > But the timer-change can also break sgmii...
>
> SGMII mode should be writing the same value to the link timer, but
> looking at it now, I see I ended up with one too many zeros on the
> 16000000! It should be 1.6ms in nanoseconds, so 1600000. Please
> correct for future testing.

tried removing 1  zero from the 16000000, but same result.
tried also setting duplex with ethtool, but  after read it is still unknown.
and i get no traffic working...i wonder because duplex was not set before your
patch too, but interface was working.

> Many thanks for your patience.

i do what i can, but i'm limited in time.

Frank