Re: [PATCH net-next v2 1/3] net: macb: fix SGMII with inband aneg disabled

[Charles Perry]

On Wed, Mar 04, 2026 at 04:23:30PM +0000, Conor Dooley wrote:
> On Wed, Mar 04, 2026 at 06:59:35AM -0800, Charles Perry wrote:
> > On Wed, Mar 04, 2026 at 11:15:43AM +0000, Conor Dooley wrote:
> > > On Tue, Feb 24, 2026 at 12:28:52PM -0800, Charles Perry wrote:
> > > > Make it possible to connect a PHY which does not use inband
> > > > autoneg to a gem MAC using phylink's information.
> > > > 
> > > > The previous implementation relied on whether or not the link
> > > > was a fixed-link to disable SGMII autoneg. This commit extend
> > > > this to all link which are not configured for inband
> > > > autonegotiation.
> > > > 
> > > > Signed-off-by: Charles Perry <charles.perry@xxxxxxxxxxxxx>
> > > 
> > > This breaks the macb on mpfs-icicle-kit, I get stuck with:
> > > 
> > > [    7.189102] mpfs-sys-controller syscontroller: Registered MPFS system controller
> > > [    7.260946] macb 20110000.ethernet eth0: PHY [20112000.ethernet-ffffffff:08] driver [Vitesse VSC8662] (irq=POLL)
> > > [    7.273881] macb 20110000.ethernet eth0: configuring for phy/sgmii link mode
> > > [    7.296580] macb 20110000.ethernet: gem-ptp-timer ptp clock registered.
> > > [    7.345782] macb 20112000.ethernet eth1: PHY [20112000.ethernet-ffffffff:09] driver [Vitesse VSC8662] (irq=POLL)
> > > [    7.358082] macb 20112000.ethernet eth1: configuring for phy/sgmii link mode
> > > [    7.380479] macb 20112000.ethernet: gem-ptp-timer ptp clock registered.
> > > [   11.376763] macb 20110000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off
> > > [   11.398403] Sending DHCP requests .
> > > [   11.472699] macb 20112000.ethernet eth1: Link is Up - 1Gbps/Full - flow control off
> > > [   13.938425] ..... timed out!
> > > [   93.598491] macb 20110000.ethernet eth0: Link is Down
> > > [   93.641823] macb 20110000.ethernet: gem-ptp-timer ptp clock unregistered.
> > > [   93.659433] macb 20112000.ethernet eth1: Link is Down
> > > [   93.691724] macb 20112000.ethernet: gem-ptp-timer ptp clock unregistered.
> > > [   93.703977] IP-Config: Retrying forever (NFS root)...
> > > [   93.758382] macb 20110000.ethernet eth0: PHY [20112000.ethernet-ffffffff:08] driver [Vitesse VSC8662] (irq=POLL)
> > > [   93.770655] macb 20110000.ethernet eth0: configuring for phy/sgmii link mode
> > > [   93.786497] macb 20110000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off
> > > [   93.795840] macb 20110000.ethernet: gem-ptp-timer ptp clock registered.
> > > [   93.844481] macb 20112000.ethernet eth1: PHY [20112000.ethernet-ffffffff:09] driver [Vitesse VSC8662] (irq=POLL)
> > > [   93.856769] macb 20112000.ethernet eth1: configuring for phy/sgmii link mode
> > > [   93.870926] macb 20112000.ethernet eth1: Link is Up - 1Gbps/Full - flow control off
> > > [   93.880302] macb 20112000.ethernet: gem-ptp-timer ptp clock registered.
> > > 
> > 
> > Hello Conor,
> > 
> > I checked the driver for the VSC8662 and it doesn't have the
> > ->inband_caps() and ->config_inband() callbacks so Linux leaves whatever
> > the bootloader puts or uses the defaults. Looking at the datasheet, this
> > should be register 23 (Extended PHY Control Set 1) bit 13 (MAC interface
> > auto-negotiation)
> > 
> > My guess is that this bit is set and since this patch disable inband
> > autonegotiation (because phylink decides it), there is a mismatch.
> > 
> > Can you add 'managed = "in-band-status"' in your device tree under the macb
> > node? That's not necessarily the fix, I just want to confirm my theory.
> 
> No, it just produces a different error:
> [    5.769864] mpfs-sys-controller syscontroller: Registered MPFS system controller
> [    5.829146] macb 20110000.ethernet eth0: Could not attach PHY (-19)
> [    5.854232] IP-Config: Failed to open eth0
> [    5.897152] macb 20112000.ethernet eth1: Could not attach PHY (-19)
> [    5.921061] IP-Config: Failed to open eth1
> [    5.925592] IP-Config: No network devices available
> [    5.938800] clk: Disabling unused clocks
> [    5.944156] PM: genpd: Disabling unused power domains
> [    5.961029] check access for rdinit=/usr/sbin/init failed: -2, ignoring
> 
> > Also '#define DEBUG' in 'drivers/net/phy/phylink.c' can help if you can
> > recompile your kernel.
> 
> Setting this provided no further logs, seemingly.
> 
> Adding some basic prints shows that the driver changed the state of the
> PCSCNTRL register from 0x1040 to 0x40, so it disabled auto neg. The
> driver previously left it as it was, 0x1040 before and 0x1040 after.
> 

Thank you for this info.

Are you able to check register 23, bit 13 of your PHY by any chance? Maybe
with the mdio/mii commands in U-Boot if you have that.

> > > and because I am NFS root, it breaks boot :)
> > > 
> > > btw, I don't see an explanation in hte commit message for why the
> > > macb_is_gem(bp) got dropped? Is this now done unconditionally when it
> > > was conditional before?
> > > 
> > 
> > Well if you get to the ->macb_pcs_config() callback, you most certainly
> > have an SGMII PCS block. Does your IP have the PCS registers? (0x200 to
> > 0x23c) Also I thought that macb doesn't do SGMII (only GEM does) so it
> > can't reach ->macb_pcs_config(). 
> 
> When I said "macb on" I meant to say "macb driver on", but omitted the
> word. Unfortunately, the idiot who added the original mpfs compatible,
> because the platform was using the "cdns,macb" compatible rather than a
> soc-specific one, did not check if the platform was actually a macb
> before doing so, and trusted the original dts author. This is actually a
> gem.

Ok, well I think its correct to remove the macb_is_gem() check in
macb_pcs_config() because if we get to that function, SGMII was picked and
macb doesn't have SGMII. Furthermore, __set_bit(PHY_INTERFACE_MODE_SGMII
...) is guarded by a macb_is_gem() so even if someone puts 'phy-mode =
"sgmii"' in their macb device tree, we shouldn't get there.

Agreed that this should have been documented in the commit message.

Regards,
Charles