Re: [PATCH net-next 0/2] net: phy: sfp: Add single-byte SMBus SFP access

From: Bjørn Mork
Date: Sun Feb 23 2025 - 13:38:50 EST

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In reply to: Maxime Chevallier: "Re: [PATCH net-next 0/2] net: phy: sfp: Add single-byte SMBus SFP access"
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Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx> writes:

> Hi everyone,
>
> Some PHYs such as the VSC8552 have embedded "Two-wire Interfaces" designed to
> access SFP modules downstream. These controllers are actually SMBus controllers
> that can only perform single-byte accesses for read and write.
>
> This series adds support for accessing SFP modules through single-byte SMBus,
> which could be relevant for other setups.
>
> The first patch deals with the SFP module access by itself, for addresses 0x50
> and 0x51.
>
> The second patch allows accessing embedded PHYs within the module with single-byte
> SMBus, adding this in the mdio-i2c driver.
>
> As raw i2c transfers are always more efficient, we make sure that the smbus accesses
> are only used if we really have no other choices.
>
> This has been tested with the following modules (as reported upon module insertion)
>
> Fiber modules :
>
> UBNT UF-MM-1G rev sn FT20051201212 dc 200512
> PROLABS SFP-1GSXLC-T-C rev A1 sn PR2109CA1080 dc 220607
> CISCOSOLIDOPTICS CWDM-SFP-1490 rev 1.0 sn SOSC49U0891 dc 181008
> CISCOSOLIDOPTICS CWDM-SFP-1470 rev 1.0 sn SOSC47U1175 dc 190620
> OEM SFP-10G-SR rev 02 sn CSSSRIC3174 dc 181201
> FINISAR CORP. FTLF1217P2BTL-HA rev A sn PA3A0L6 dc 230716
> OEM ES8512-3LCD05 rev 10 sn ESC22SX296055 dc 220722
> SOURCEPHOTONICS SPP10ESRCDFF rev 10 sn E8G2017450 dc 140715
> CXR SFP-STM1-MM-850 rev 0000 sn K719017031 dc 200720
>
> Copper modules
>
> OEM SFT-7000-RJ45-AL rev 11.0 sn EB1902240862 dc 190313
> FINISAR CORP. FCLF8521P2BTL rev A sn P1KBAPD dc 190508
> CHAMPION ONE 1000SFPT rev - sn GBC59750 dc 19110401
>
> DAC :
>
> OEM SFP-H10GB-CU1M rev R sn CSC200803140115 dc 200827
>
> In all cases, read/write operations happened without errors, and the internal
> PHY (if any) was always properly detected and accessible
>
> I haven't tested with any RollBall SFPs though, as I don't have any, and I don't
> have Copper modules with anything else than a Marvell 88e1111 inside. The support
> for the VSC8552 SMBus may follow at some point.
>
> Thanks,
>
> Maxime
>
> Maxime Chevallier (2):
> net: phy: sfp: Add support for SMBus module access
> net: mdio: mdio-i2c: Add support for single-byte SMBus operations
>
> drivers/net/mdio/mdio-i2c.c | 79 ++++++++++++++++++++++++++++++++++++-
> drivers/net/phy/sfp.c | 65 +++++++++++++++++++++++++++---
> 2 files changed, 138 insertions(+), 6 deletions(-)

Nice! Don't know if you're aware, but OpenWrt have had patches for
SMBus access to SFPs for some time:

https://github.com/openwrt/openwrt/blob/main/target/linux/realtek/patches-6.6/714-net-phy-sfp-add-support-for-SMBus.patch
https://github.com/openwrt/openwrt/blob/main/target/linux/realtek/patches-6.6/712-net-phy-add-an-MDIO-SMBus-library.patch

The reason they carry these is that they support Realtek rtl930x based
switches. The rtl930x SoCs include an 8 channel SMBus host which is
typically connected to any SFP+ slots on the switch.

There has been work going on for a while to bring the support for these
SoCs to mainline, and the SMBus host driver is already here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/i2c/busses/i2c-rtl9300.c?id=c366be720235301fdadf67e6f1ea6ff32669c074

I assume DSA and ethernet eventually will follow, making SMBus SFP
support necessary for this platform too.

So thanks for doing this!

FWIW, I don't think the OpenWrt mdio patch works at all. I've recently
been playing with an 8 SFP+ port switch based on rtl9303, and have tried
to fixup both the clause 22 support and add RollBall and clause 45.
This is still a somewhat untested hack, and I was not planning on
presenting it here as such, but since this discussion is open:
https://github.com/openwrt/openwrt/pull/17950/commits/c40387104af62a065797bc3e23dfb9f36e03851b

Sorry for the format. This is a patch for the patch already present in
OpenWrt. Let me know if you want me to post the complete patched
mdio-smbus.c for easier reading.

The main point I wanted to make is that we also need RollBall and clause
45 over SMBus. Maybe not today, but at some point. Ideally, the code
should be shared with the i2c implementation, but I found that very hard
to do as it is.

As for Russel's comments regarding atomic reads, I'm hoping for the
pragmatic approach and allow all possible features over SMBus. It's not
like we have the option of using i2c on a host which only supports
SMBus. My experience is that both hwmon and phy access works pretty
well with SMBus byte accesses.

Some examples:

root@s508cl:~# ethtool -m lan1
Identifier : 0x03 (SFP)
Extended identifier : 0x04 (GBIC/SFP defined by 2-wire interface ID)
Connector : 0x07 (LC)
Transceiver codes : 0x10 0x00 0x00 0x00 0x00 0x00 0x06 0x00 0x00
Transceiver type : 10G Ethernet: 10G Base-SR
Transceiver type : FC: Multimode, 50um (M5)
Encoding : 0x03 (NRZ)
BR, Nominal : 10300MBd
Rate identifier : 0x00 (unspecified)
Length (SMF,km) : 0km
Length (SMF) : 0m
Length (50um) : 300m
Length (62.5um) : 300m
Length (Copper) : 0m
Length (OM3) : 300m
Laser wavelength : 850nm
Vendor name : OEM
Vendor OUI : 00:00:00
Vendor PN : SFP-10G-SR
Vendor rev : B
Option values : 0x00 0x1a
Option : RX_LOS implemented
Option : TX_FAULT implemented
Option : TX_DISABLE implemented
BR margin, max : 0%
BR margin, min : 0%
Vendor SN : 202412240025
Date code : 241224
Optical diagnostics support : Yes
Laser bias current : 7.146 mA
Laser output power : 0.4005 mW / -3.97 dBm
Receiver signal average optical power : 0.5088 mW / -2.93 dBm
Module temperature : 52.13 degrees C / 125.83 degrees F
Module voltage : 3.2644 V
Alarm/warning flags implemented : Yes
Laser bias current high alarm : Off
Laser bias current low alarm : Off
Laser bias current high warning : Off
Laser bias current low warning : Off
Laser output power high alarm : Off
Laser output power low alarm : Off
Laser output power high warning : Off
Laser output power low warning : Off
Module temperature high alarm : Off
Module temperature low alarm : Off
Module temperature high warning : Off
Module temperature low warning : Off
Module voltage high alarm : Off
Module voltage low alarm : Off
Module voltage high warning : Off
Module voltage low warning : Off
Laser rx power high alarm : Off
Laser rx power low alarm : Off
Laser rx power high warning : Off
Laser rx power low warning : Off
Laser bias current high alarm threshold : 12.000 mA
Laser bias current low alarm threshold : 1.000 mA
Laser bias current high warning threshold : 10.000 mA
Laser bias current low warning threshold : 2.000 mA
Laser output power high alarm threshold : 1.5849 mW / 2.00 dBm
Laser output power low alarm threshold : 0.1000 mW / -10.00 dBm
Laser output power high warning threshold : 1.2589 mW / 1.00 dBm
Laser output power low warning threshold : 0.1259 mW / -9.00 dBm
Module temperature high alarm threshold : 85.00 degrees C / 185.00 degrees F
Module temperature low alarm threshold : -10.00 degrees C / 14.00 degrees F
Module temperature high warning threshold : 80.00 degrees C / 176.00 degrees F
Module temperature low warning threshold : -5.00 degrees C / 23.00 degrees F
Module voltage high alarm threshold : 3.7000 V
Module voltage low alarm threshold : 2.9000 V
Module voltage high warning threshold : 3.6000 V
Module voltage low warning threshold : 3.0000 V
Laser rx power high alarm threshold : 1.9953 mW / 3.00 dBm
Laser rx power low alarm threshold : 0.0398 mW / -14.00 dBm
Laser rx power high warning threshold : 1.5849 mW / 2.00 dBm
Laser rx power low warning threshold : 0.0501 mW / -13.00 dBm

root@s508cl:~# ethtool -m lan3
Identifier : 0x03 (SFP)
Extended identifier : 0x04 (GBIC/SFP defined by 2-wire interface ID)
Connector : 0x07 (LC)
Transceiver codes : 0x10 0x00 0x00 0x00 0x40 0x00 0x0c 0x00 0x00
Transceiver type : 10G Ethernet: 10G Base-SR
Transceiver type : FC: short distance (S)
Transceiver type : FC: Multimode, 62.5um (M6)
Transceiver type : FC: Multimode, 50um (M5)
Encoding : 0x06 (64B/66B)
BR, Nominal : 10300MBd
Rate identifier : 0x00 (unspecified)
Length (SMF,km) : 0km
Length (SMF) : 0m
Length (50um) : 30m
Length (62.5um) : 10m
Length (Copper) : 0m
Length (OM3) : 0m
Laser wavelength : 850nm
Vendor name : FS
Vendor OUI : 00:00:00
Vendor PN : SFP-10G-T
Vendor rev :
Option values : 0x00 0x1a
Option : RX_LOS implemented
Option : TX_FAULT implemented
Option : TX_DISABLE implemented
BR margin, max : 10%
BR margin, min : 88%
Vendor SN : F2220644072
Date code : 220824
Optical diagnostics support : Yes
Laser bias current : 6.000 mA
Laser output power : 0.5000 mW / -3.01 dBm
Receiver signal average optical power : 0.0000 mW / -inf dBm
Module temperature : 54.22 degrees C / 129.59 degrees F
Module voltage : 3.3368 V
Alarm/warning flags implemented : Yes
Laser bias current high alarm : Off
Laser bias current low alarm : Off
Laser bias current high warning : Off
Laser bias current low warning : Off
Laser output power high alarm : Off
Laser output power low alarm : Off
Laser output power high warning : Off
Laser output power low warning : Off
Module temperature high alarm : Off
Module temperature low alarm : Off
Module temperature high warning : Off
Module temperature low warning : Off
Module voltage high alarm : Off
Module voltage low alarm : Off
Module voltage high warning : Off
Module voltage low warning : Off
Laser rx power high alarm : Off
Laser rx power low alarm : On
Laser rx power high warning : Off
Laser rx power low warning : On
Laser bias current high alarm threshold : 15.000 mA
Laser bias current low alarm threshold : 1.000 mA
Laser bias current high warning threshold : 13.000 mA
Laser bias current low warning threshold : 2.000 mA
Laser output power high alarm threshold : 1.9952 mW / 3.00 dBm
Laser output power low alarm threshold : 0.1584 mW / -8.00 dBm
Laser output power high warning threshold : 1.5848 mW / 2.00 dBm
Laser output power low warning threshold : 0.1778 mW / -7.50 dBm
Module temperature high alarm threshold : 80.00 degrees C / 176.00 degrees F
Module temperature low alarm threshold : -10.00 degrees C / 14.00 degrees F
Module temperature high warning threshold : 75.00 degrees C / 167.00 degrees F
Module temperature low warning threshold : -5.00 degrees C / 23.00 degrees F
Module voltage high alarm threshold : 3.6000 V
Module voltage low alarm threshold : 3.0000 V
Module voltage high warning threshold : 3.5000 V
Module voltage low warning threshold : 3.1000 V
Laser rx power high alarm threshold : 1.1220 mW / 0.50 dBm
Laser rx power low alarm threshold : 0.0199 mW / -17.01 dBm
Laser rx power high warning threshold : 1.0000 mW / 0.00 dBm
Laser rx power low warning threshold : 0.0223 mW / -16.52 dBm

root@s508cl:~# ethtool -m lan8
Identifier : 0x03 (SFP)
Extended identifier : 0x04 (GBIC/SFP defined by 2-wire interface ID)
Connector : 0x07 (LC)
Transceiver codes : 0x10 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
Transceiver type : 10G Ethernet: 10G Base-SR
Encoding : 0x06 (64B/66B)
BR, Nominal : 10300MBd
Rate identifier : 0x00 (unspecified)
Length (SMF,km) : 0km
Length (SMF) : 0m
Length (50um) : 80m
Length (62.5um) : 20m
Length (Copper) : 0m
Length (OM3) : 300m
Laser wavelength : 0nm
Vendor name : OEM
Vendor OUI : 00:00:00
Vendor PN : SFP-10G-T8
Vendor rev : A
Option values : 0x00 0x1a
Option : RX_LOS implemented
Option : TX_FAULT implemented
Option : TX_DISABLE implemented
BR margin, max : 0%
BR margin, min : 0%
Vendor SN : F250114T0010
Date code : 250115
Optical diagnostics support : Yes
Laser bias current : 6.000 mA
Laser output power : 0.5010 mW / -3.00 dBm
Receiver signal average optical power : 0.5010 mW / -3.00 dBm
Module temperature : 67.64 degrees C / 153.75 degrees F
Module voltage : 3.2538 V
Alarm/warning flags implemented : Yes
Laser bias current high alarm : Off
Laser bias current low alarm : Off
Laser bias current high warning : Off
Laser bias current low warning : Off
Laser output power high alarm : Off
Laser output power low alarm : Off
Laser output power high warning : Off
Laser output power low warning : Off
Module temperature high alarm : Off
Module temperature low alarm : Off
Module temperature high warning : Off
Module temperature low warning : Off
Module voltage high alarm : Off
Module voltage low alarm : Off
Module voltage high warning : Off
Module voltage low warning : Off
Laser rx power high alarm : Off
Laser rx power low alarm : Off
Laser rx power high warning : Off
Laser rx power low warning : Off
Laser bias current high alarm threshold : 15.000 mA
Laser bias current low alarm threshold : 1.000 mA
Laser bias current high warning threshold : 13.000 mA
Laser bias current low warning threshold : 2.000 mA
Laser output power high alarm threshold : 1.1220 mW / 0.50 dBm
Laser output power low alarm threshold : 0.1862 mW / -7.30 dBm
Laser output power high warning threshold : 1.0000 mW / 0.00 dBm
Laser output power low warning threshold : 0.2344 mW / -6.30 dBm
Module temperature high alarm threshold : 80.00 degrees C / 176.00 degrees F
Module temperature low alarm threshold : -10.00 degrees C / 14.00 degrees F
Module temperature high warning threshold : 75.00 degrees C / 167.00 degrees F
Module temperature low warning threshold : -5.00 degrees C / 23.00 degrees F
Module voltage high alarm threshold : 3.5999 V
Module voltage low alarm threshold : 2.9000 V
Module voltage high warning threshold : 3.5000 V
Module voltage low warning threshold : 3.0000 V
Laser rx power high alarm threshold : 1.1220 mW / 0.50 dBm
Laser rx power low alarm threshold : 0.0645 mW / -11.90 dBm
Laser rx power high warning threshold : 1.0000 mW / 0.00 dBm
Laser rx power low warning threshold : 0.0812 mW / -10.90 dBm

Phy access works too:

root@s508cl:~# mdio smbus:sfp-p5 phy 22
BMCR(0x00): 0x1140
flags: -reset -loopback +aneg-enable -power-down -isolate -aneg-restart
-collision-test
speed: 1000-full

BMSR(0x01): 0x7949
capabilities: -100-t4 +100-tx-f +100-tx-h +10-t-f +10-t-h -100-t2-f -100-t2-h
flags: +ext-status -aneg-complete -remote-fault +aneg-capable -link
-jabber +ext-register

ID(0x02/0x03): 0x01410cc2

ESTATUS(0x0F): 0xf000
capabilities: +1000-x-f +1000-x-h +1000-t-f +1000-t-h

Even this, which is using RollBall over SMBus:

root@s508cl:~# mdio smbus:sfp-p3 mmd 17:1
CTRL1(0x00): 0x0002
flags: -reset -low-power +remote-loopback -local-loopback
speed: 10

STAT1(0x01): 0x0002
capabilities: -pias -peas +low-power
flags: -fault -link

DEVID(0x02/0x03): 0x31c31c12

SPEED(0x04): 0x6031
capabilities: -400g +5g +2.5g -200g -25g -10g-xr -100g -40g -10g/1g -10 +100
+1000 -10-ts -2-tl +10g

DEVS(0x06/0x05): 0xe000009a
devices: +vendor2 +vendor1 +c22-ext -power-unit -ofdm -pma4 -pma3 -pma2 -pma1
+aneg -tc -dte-xs +phy-xs +pcs -wis +pma/pmd -c22

CTRL2(0x07): 0x0009
flags: -pias -peas
type: 10g-t

STAT2(0x08): 0xb301
capabilities: +tx-fault +rx-fault +ext-register +tx-disable +local-loopback
-10g-sr -10g-lr -10g-er -10g-lx4 -10g-sw -10g-lw -10g-ew
flags: +present -tx-fault -rx-fault

EXTABLE(0x0B): 0x40fc
capabilities: -10g-cx4 -10g-lrm +10g-t +10g-kx4 +10g-kr +1000-t +1000-kx
+100-tx -10-t -p2mp -40g/100g -1000/100-t1 -25g -200g/400g
+2.5g/5g -1000-h

PKGID(0x0E/0x0F): 0x31c31c12

Bjørn

Next message: Mike Rapoport: "Re: [PATCH v4 05/14] kexec: Add Kexec HandOver (KHO) generation helpers"
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In reply to: Maxime Chevallier: "Re: [PATCH net-next 0/2] net: phy: sfp: Add single-byte SMBus SFP access"
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