Re: [PATCH net-next v2 0/3] net: phy: dp83869: Support 1000Base-X SFP

Hi Álvaro,

On Friday, 13 February 2026 13:31:17 CEST Álvaro G. M. wrote:

On Mon, 10 Nov 2025 10:24:52 +0100

Romain Gantois [off-list ref] wrote:

quoted

Hi everyone,

This is version two of my series which adds support for using the
DP83869 PHY as a transceiver between an RGMII upper MAC and a
downstream 1000Base-X SFP module.

Hi Romain,

I am quite interested in this too, as we have a new version of a PCB in
which we replaced a dp83848 (which only works with 100base-tx) with
dp83869 with the intent of using 1000base-sx or similar SFPs.

The are two different SFPs that I was able to use with dp83848 and
would like to use them with the dp83869 as well:

- RJ45 based:
    - Robofiber SFP-5000-RJ45A: 10/100Base-Tx SFP RJ45
    - H!Fiber ASF-GE-T1 1000Base-T SFP RJ-25

Both of these already work with dp83869 with kernel 6.12, provided I
set mode to DP83869_RGMII_100_BASE. If I try to make the 1000Base-T
work at 1Gbps by setting op mode to DP83869_RGMII_1000_BASE it will
still set speed to 100Mbps and will work just fine, but if I try to set
speed to 1000, all data transfer stops.

Personally, I could live with this, but I assume it should be possible
for this SFP to work at 1Gbps.

I can't speak for this particular SFP module, but I've managed to make the 
DP83869 work at near-1Gbps with my modules.

- Fiber based:
    - CISCO-FINISAR G155B3520KCD which I believe reports bit
    
      ETHTOOL_LINK_MODE_10000baseSR_Full_BIT
    
    - AVAGO AFBR-709SMZ which reports as 10gbase-r
    - ATGBICS AFBR-5710ALZ-C 1000BASE-SX

The first two, even if they report as 10Gbase, did work with dp83848 at
100Mbps out of the box, but do not seem to work in any case with
dp83869. The last one, 1000base-sx, is the one that I expected to
work either out of the box or by using this set of patches of yours.
However, none of them do work.

What I did next, as the 10gbase was simply refused, was to apply the
following patch above your series, which is more or less based on one
of your previous patches from 2025. The key here is that I try hard to
fallback to 100Mbps on every instance of non working SFP. So, I need
that if linkmode_empty(sfp_support) because the 10/100 SFPs simply do
not have any bit active to signal that capability, and I also set mode
to RGMII_100_BASE in every case. So, with this patch:

sfp amba_pl:sfp: module AVAGO            AFBR-709SMZ      rev G4.1 sn
AA17053045F      dc 170204
TI DP83869 axienet-40c00000:01: dp83869_module_insert SFP compatible link
mode: 10gbase-r
TI DP83869 axienet-40c00000:01: incompatible PHY-to-SFP module link mode
10gbase-r! Try simply 10/100
Configuring network: xilinx_axienet 40c00000.ethernet eth0: PHY [axienet-
40c00000:01] driver [TI DP83869] (irq=POLL)
xilinx_axienet 40c00000.ethernet eth0: configuring for phy/1000base-x link
mode xilinx_axienet 40c00000.ethernet eth0: Link is Up - 100Mbps/Full -
flow control off

And finally I have my other device answer to ping! So it seems that the
DP83869, as is, won't be able to run at 1Gbps no matter what.

From the datasheet... wouldn't it be necessary to update OP_MODE_DECODE
Register (Offset = 1DFh) [Reset = 0040h] CFG_OPMODE bits 2-0 to set value 1
RGMII to 1000Base-X?

This is done by dp83869_configure_mode() when the relevant SFP module is 
inserted.

Thanks,

-- 
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com