On 10/02/2026 23:12, Benjamin Larsson wrote:
If I understand correct, the ref SDK just sets up a transparent bridge
and lets the packets flow through? If that is correct is that an
option here?
When use_soc_lan is unset, this is what happens. When use_soc_lan is
set, it does a bunch of highly awkward stuff to add support for one
extra port on the internal switch. It's an option, probably to treat the
internal switch as part of the eth driver - however this will not work
on EN7526C which no external switch, internal is exposed.
And IMO we should not stack stags. If it is possible to pass stags
through with the pass-through bit intact it should be possible to
address all ports on both switches with just one stag.
I was hoping the PT_OPTION PVC bit would set the stag pass through bit
on incoming frames.
Stacking stags does potentially have a performance penalty in the tag
parser - I say "potentially" because it's already walking a list which
could be an array index, and even 2 array indexes is faster than what we
have now.
But trying to use the PT bit as designed makes it impossible to
differentiate between a packet that came from port N of the external
switch and a packet that came from port N of the internal. Vendor code
doesn't support having the same port number active on both internal and
external, if you try it will quietly overwrite the switch_port_map entry
in init_ethernet_port_map(), so I surmise this is a real silicon bug,
not a misconfiguration on my end.
But (so far), stacking tags seems to work, so I would much prefer it to
inter-switch rules, i.e. "you can't enable this port in the DT because
you have one with the same number on the other switch".
BTW Vendor code (see: TCSUPPORT_MULTI_SWITCH_EXT) suggests there are
boards with multiple external switches. Probably a board integrator hung
another 7530 off of one of the RGMII interfaces. Per my reading, vendor
code falls back on VLANs, giving up on the stag entirely. I haven't
confirmed that transmit works yet, but assuming it does, stacked stags
should Just Work in this use case whereas the PT bit clearly would not.
Thanks,
Caleb
MvH
Benjamin Larsson
On 10/02/2026 22:07, Caleb James DeLisle wrote:
Welp, that didn't take long.
It turns out when I remove PORT_STAG on the receiving side (internal
port 5), the switch mistakes the first 2 bytes of the stag for a
length, and if the packet is actually shorter than that length, it
drops. So 0004 worked fine, but 0104 didn't until I sent a longer
packet.
Clearing L2LEN_CHK on the AGC register works around the issue and
packets are received in full with correctly stacked stags.
If I can make the passthrough bit copy, or stop it from copying the
port number when I have PORT_STAG set, that would be of course
superior, but if I have to use the hack to get the feature then I'll
send the patchset like that.
Thanks,
Caleb
On 10/02/2026 20:25, Caleb James DeLisle wrote:
Hello guys,
I have an update on this MT7530. As I mentioned in my initial email
there are two switches that are stacked, so I'm needing to do quite
a bit of patching to mt7530.c to create anything that is going to work.
I'm trying to handle incoming traffic from the MCM ("external")
switch to the on-die switch. It comes in port 4 of the external,
where I have a cable attached, then goes to port 6 which the
external is treating as a CPU port. Then it comes in port 5 of the
internal. Here's my values for the PVC register:
ext 4 0x810001c0 ACC_FRM=all VLAN_ATTR=transparent EG_TAG=consistent
STAG_VPID=0x8100
ext 6 0x00000920 ACC_FRM=all PORT_STAG VLAN_ATTR=user
EG_TAG=consistent PT_OPTION STAG_VPID=0x0
int 5 0x810001e0 ACC_FRM=all PORT_STAG VLAN_ATTR=transparent
EG_TAG=consistent STAG_VPID=0x8100
int 6 0x00000120 ACC_FRM=all PORT_STAG VLAN_ATTR=user
EG_TAG=consistent STAG_VPID=0x0
When PT_OPTION is set on port 6 of the external, it sets the
Passthrough bit on the Special Tag before sending it to the internal
switch. When int 5 has PORT_STAG set, the Passthrough bit is
required otherwise it will drop STAG'd packets. However, when it's
set the switch does a weird stupid thing and it copies the port
number from what was received from the external switch - but it
DOESN'T copy the passthrough bit. So you end up with this:
[ port 4 ][ port 4 +PT ][ packet header ]
And the obvious problem is this is indistinguishable from a packet
that comes from port 4 of the internal switch and has an stag
directly under the eth header.
---
Another angle is to remove the PORT_STAG from internal port 5, and
then you get this:
[ port 5 ][ port 4 +PT ][ packet header ]
In that case you can also remove PT_OPTION from external port 6, but
sending ANY kind of VLAN packet from the outside gets it filtered
and RxFiltering gets incremented. No matter what I do, I can't
figure out how to stop VLAN packets from getting dropped except by
putting PORT_STAG on the receiving port (internal port 5). No
configuration of internal port6 prevents it, even if it's a dumb
switch, is still drops them.
Anyone have any ideas?
Thanks,
Caleb
On 28/01/2026 14:26, Caleb James DeLisle wrote:
Update: It turns out the reset controller I was using only reset
the on-die switch, Benjamin found the reset register for the
external switch and now everything is behaving MUCH more like
normal. I'd say at this point I'm no longer stuck.
Thanks,
Caleb
On 27/01/2026 18:26, Caleb James DeLisle wrote:
Would there be any reason not to set BMCR_PDOWN in
mt7530_phy_config_init() so we know they're in a consistent state?
Also if you happen to have an MT7621 sitting there running, would
you mind setting BMCR_ANENABLE | BMCR_ANRESTART with mdio on a
running port to see if it's the same behavior? The port should
immediately die and then go into a loop trying to connect every
few seconds / minutes depending on what it's connected to.
Whoops, spoke too soon. dsa_register_switch() (indirectly) calls
phy_resume() so the phy is up while the port is down. However,
adding this to mt7530_port_enable() does make it work:
if (priv->id == ID_EN751221_EXT && phy)
genphy_soft_reset(phy);
I note that if the port is brought up within seconds of having
been reset, then it seems to work (at least sporadically) despite
the BMCR_ANENABLE bug. I imagine this is something that can be
tuned out, but given it's happening in the bootloader, I don't
have much confidence that I'm going to find the knob to fix it.
I've got a problem with my vendor OS image, but when I get that
fixed I'll check that as well.
In the mean time, if any likely culprits come to mind, do let me
know.
Thanks,
Caleb
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