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

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Message-ID: <ihxsrolj75ufuhyfu4r2dalth4dzkmamh5naat5fa74iwu3mrb@5vl453qcsoj7>
Date: Mon, 24 Feb 2025 11:36:16 +0100
From: Marek Behún <kabel@...nel.org>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Bjørn Mork <bjorn@...k.no>, davem@...emloft.net, 
	Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Russell King <linux@...linux.org.uk>, Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com, 
	Florian Fainelli <f.fainelli@...il.com>, Köry Maincent <kory.maincent@...tlin.com>, 
	Simon Horman <horms@...nel.org>, Romain Gantois <romain.gantois@...tlin.com>, 
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH net-next 0/2] net: phy: sfp: Add single-byte SMBus SFP
 access

On Mon, Feb 24, 2025 at 10:38:14AM +0100, Maxime Chevallier wrote:
> Hi Bjørn,
> 
> On Sun, 23 Feb 2025 19:37:05 +0100
> Bjørn Mork <bjorn@...k.no> wrote:
> 
> > Maxime Chevallier <maxime.chevallier@...tlin.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!
> 
> Good to know this is useful to you ! So there's at least 2 different
> classes of products out there with SMBus that advertise that it's
> "designed for SFP" ._.
> 
> > 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.
> 
> I don't have anything to test that, and yeah that can be considered as
> a second step, however I don't even know if this can work at all with
> single byte accesses :(

I will send you some RollBall modules, Maxime.

Marek