Re: [PATCH] optoe: driver to read/write SFP/QSFP EEPROMs
From: Don Bollinger
Date: Mon Jun 11 2018 - 17:20:28 EST
On Mon, Jun 11, 2018 at 01:33:07PM -0500, Tom Lendacky wrote:
> On 6/10/2018 11:25 PM, Don Bollinger wrote:
> > optoe is an i2c based driver that supports read/write access to all
> > the pages (tables) of MSA standard SFP and similar devices (conforming
> > to the SFF-8472 spec) and MSA standard QSFP and similar devices
> > (conforming to the SFF-8436 spec).
> > These devices provide identification, operational status and control
> > registers via an EEPROM model. These devices support one or 3 fixed
> > pages (128 bytes) of data, and one page that is selected via a page
> > register on the first fixed page. Thus the driver's main task is
> > to map these pages onto a simple linear address space for user space
> > management applications. See the driver code for a detailed layout.
> > EEPROM data is accessible via a bin_attribute file called 'eeprom',
> > e.g. /sys/bus/i2c/devices/24-0050/eeprom.
> > Signed-off-by: Don Bollinger <don@xxxxxxxxxxxxxxxxx>
> > ---
> > Why should this driver be in the Linux kernel? SFP and QSFP devices plug
> > into switches to convert electrical to optical signals and drive the
> > optical signal over fiber optic cables. They provide status and control
> > registers through an i2c interface similar to to other EEPROMS. However,
> > they have a paging mechanism that is unique, which requires a different
> > driver from (for example) at24. Various drivers have been developed for
> > this purpose, none of them support both SFP and QSFP, provide both read
> > and write access, and access all 256 architected pages. optoe does all
> > of these.
> > optoe has been adopted and is shipping to customers as a base module,
> > available to all platforms (switches) and used by multiple vendors and
> > platforms on both ONL (Open Network Linux) and SONiC (Microsoft's
> > 'Software for Open Networking in the Cloud').
> > This patch has been built on the latest staging-testing kernel. It has
> > built and tested with SFP and QSFP devices on an ARM platform with a 4.9
> > kernel, and an x86 switch with a 3.16 kernel. This patch should install
> > and build clean on any kernel from 3.16 up to the latest (as of 6/10/2018).
> > Documentation/misc-devices/optoe.txt | 56 ++
> > drivers/misc/eeprom/Kconfig | 18 +
> > drivers/misc/eeprom/Makefile | 1 +
> > drivers/misc/eeprom/optoe.c | 1141 ++++++++++++++++++++++++++++++++++
> > 4 files changed, 1216 insertions(+)
> > create mode 100644 Documentation/misc-devices/optoe.txt
> > create mode 100644 drivers/misc/eeprom/optoe.c
> There's an SFP driver under drivers/net/phy. Can that driver be extended
> to provide this support? Adding Russel King who developed sfp.c, as well
> at the netdev mailing list.
I don't think that would work very well. It's software, anything is
sfp.c appears to be working with mdio, gpio and 'sfp_bus', in addition
to i2c. optoe only access the EEPROM, and only via i2c. The linux
standard i2c interfaces are the only dependencies for optoe.
Also, sfp.c does not support QSFP (best I can tell), and it does not
support additional pages beyond the 256 bytes at i2c address 0x50 and
Best I can tell, sfp.c supports SFP devices on NIC cards. Those cards
have a very different hardware architecture from the network switches
that optoe is targeting.