I2C Hotplugging

Hi MoonDrop,

No, I2C does not support HW/SW hot-plug. See the below pointers for more details:

e2e.ti.com/.../1788135
www.ctrlinux.com/.../

Regards,
Pavel

Ok :(
The thing is that we have a SFP interface (hot-pluggable by definition) which requires a serial 2-wire connection (stated in SFP MSA).
The only interface we found suitable for it is the omap_i2c. Do you have maybe a suggestion on which interface can we use instead of I2C for it?

MoonDrop,

What is SFP? Is it Small Form-factor Pluggable module? Can you provide its datasheet?

You can use i2c-tools (i2cdetect, i2cdump, i2cset, i2cget) (after you hot plug SFP on I2C bus) to detect and use the SFP module:

processors.wiki.ti.com/.../Linux_Core_I2C_User's_Guide
processors.wiki.ti.com/.../Processor_SDK_Linux_Training:_Introduction_to_Device_Driver_Development

Regards,
Pavel

Yes. SFP is small Form-factor.
It does not have a datasheet, because each module (plug) is from different vendor. The SFP is only the interface for the physical media. Part of it's requirements is 100Khz 2-wire serial to communicate with the EEPROM or/and PHY of the plugged module.
The module can be inserted/removed in hotplug manner.
Here is the link for the SFP specification we implemented: ftp.seagate.com/.../INF-8074.PDF

MoonDrop said:

Part of it's requirements is 100Khz 2-wire serial to communicate with the EEPROM or/and PHY of the plugged module.

Are these 2 wires clock and data?

MoonDrop said:

Here is the link for the SFP specification we implemented: ftp.seagate.com/.../INF-8074.PDF

I can not access this link. Can you provide it again?

Regards,
Pavel

Hi. 

Yes these wires are clock and data. I don't why the link is down, but I attach here the file anyway

SFP MSA.pdf

MoonDrop,

I2C should be use, I do not see another option. I found one example that use SFP with Pi and i2c-tools:

eoinpk.blogspot.bg/.../raspberry-pi-and-programming-eeproms-on.html

Regards,
Pavel

Hi.

We are actually already using it. The problem (and why I asked about hot plug in the first place) is that sometimes (about 1 to 10) times. When we hot-plug the SFP module into the slot, we get a kernel error on the i2c bus (i2c bus 2) which is unrecoverable. The messages: "omap_i2c omap_i2c.2: timeout waiting for bus ready" keeps coming to the console, there is no communication with the devices on the bus (i2c-detect also hangs on each address) and will only stop by reboot. Here is the log:

root@dm814x-evm:~# [  141.705982] PHY: 0:02 - Link is Up - 1000/Full
[  143.715153] PHY: 0:02 - Link is Down
[  145.341878] cpsw cpsw.0: eth1: Link is Up - 100Mbps/Full - flow control off
[  155.726013] PHY: 0:02 - Link is Up - 1000/Full
[  157.756193] PHY: 0:02 - Link is Down
[  158.541394] omap_i2c omap_i2c.2: Arbitration lost
[  158.546918] mdio_bus i2c:sfp.1: i2c_mii_read Error -5 reading bus SFP I2C Bus addr 0x56 reg 0x01
[  159.639979] omap_i2c omap_i2c.2: timeout waiting for bus ready
[  159.654092] mdio_bus i2c:sfp.1: i2c_mii_read error, needed 2 got -110

We have nothing else on this bus, it is dedicated for SFP only. Do you have any idea where that might come from (hotplugging??) or how is possible to fix (and better avoid) while running without rebooting?

Thank you very much :)