| Message ID | 20250223172848.1098621-1-maxime.chevallier@bootlin.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | net: phy: sfp: Add single-byte SMBus SFP access | expand |
On Sun, Feb 23, 2025 at 06:28:45PM +0100, Maxime Chevallier wrote: > 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 goes against SFF-8472, and likely breaks atomic access to 16-bit PHY registers. For the former, I quote from SFF-8472: "To guarantee coherency of the diagnostic monitoring data, the host is required to retrieve any multi-byte fields from the diagnostic monitoring data structure (e.g. Rx Power MSB - byte 104 in A2h, Rx Power LSB - byte 105 in A2h) by the use of a single two-byte read sequence across the 2-wire interface." So, if using a SMBus controller, I think we should at the very least disable exporting the hwmon parameters as these become non-atomic reads. Whether PHY access works correctly or not is probably module specific. E.g. reading the MII_BMSR register may not return latched link status because the reads of the high and low bytes may be interpreted as two seperate distinct accesses. In an ideal world, I'd prefer to say no to hardware designs like this, but unfortunately, hardware designers don't know these details of the protocol, and all they see is "two wire, oh SMBus will do".
Hi Russell On Sun, 23 Feb 2025 17:40:37 +0000 "Russell King (Oracle)" <linux@armlinux.org.uk> wrote: > On Sun, Feb 23, 2025 at 06:28:45PM +0100, Maxime Chevallier wrote: > > 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 goes against SFF-8472, and likely breaks atomic access to 16-bit > PHY registers. > > For the former, I quote from SFF-8472: > > "To guarantee coherency of the diagnostic monitoring data, the host is > required to retrieve any multi-byte fields from the diagnostic > monitoring data structure (e.g. Rx Power MSB - byte 104 in A2h, Rx > Power LSB - byte 105 in A2h) by the use of a single two-byte read > sequence across the 2-wire interface." > > So, if using a SMBus controller, I think we should at the very least > disable exporting the hwmon parameters as these become non-atomic > reads. That makes sense to me, it's best-effort at that point :) > Whether PHY access works correctly or not is probably module specific. > E.g. reading the MII_BMSR register may not return latched link status > because the reads of the high and low bytes may be interpreted as two > seperate distinct accesses. > > In an ideal world, I'd prefer to say no to hardware designs like this, > but unfortunately, hardware designers don't know these details of the > protocol, and all they see is "two wire, oh SMBus will do". On that particular PHY I'm mentionning, the feature really is advertised to HW designers as "you connect that TWI to your SFP cage and you're good". I was very surprised as well when digging deeper and figuring that not only it's SMBus, and worse, 1-byte accesses only... However there are already some HW out there with this feature in use. If this is OK for you to accept that as a "best effort, degraded mode as there's no hwmon", that's already great :) Thanks for being so quick ! Maxime
Maxime Chevallier <maxime.chevallier@bootlin.com> 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
On Sun, Feb 23, 2025 at 07:37:05PM +0100, Bjørn Mork wrote: > 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. The pragmatic approach is to avoid using things that are unsafe (and thus unreliable.) As I said, disabling hwmon makes sense because you don't want to read the 16-bit values non-atomically and end up with scrambled readings that then trigger alarms because they've exceeded the thresholds. Merely proving that "oh look it works because I can read stuff" doesn't address my point. SMBus being used is as bad as all those crappy SFP modules out there that don't conform to the SFP MSA but claim they do. It's just yet another hardware designer cocking the design up in a way that makes SFPs unreliable. Unfortunately, there's not much that we can do to influence that, but not publishing stuff that's ultimately unreliable helps to make the issue known. So, not only do I think that hwmon should be disabled if using SMBus, but I also think that the kernel should print a warning that SMBus is being used and therefore e.g. copper modules will be unreliable. We don't know how the various firmwares in various microprocessors that convert I2C to MDIO will behave when faced with SMBus transfers. All in all, I'm not happy with this, and I do wish hardware designers would get a clue.