ixgbe: add MDIO access routines from intel DPDK

[adrian]

Summary

These are from Intel DPDK sources, which are BSD 3 claused licenced.

[adrian]

So although not needed for etherswitch support, it is here for completeness.

This is (a) clause 45 only, (b) limited to the existing phy/mdi path that hard-codes the PHY address based on the NIC instance, and (c) isn't tied into the MDIO bus path in D50128.

I believe that this is to support a normal external clause 45 PHY attached to the backplane.

[erj]

sys/dev/ixgbe/ixgbe_x550.c

546

My only nit here is that both ixgbe_read_phy_reg_x550em() and this function could be laid out the same way (e.g. just return early when you can't acquire the FW/SW semaphore), but they aren't?

[erj]

I'm going to assume there are some hidden #ifdefs that are getting stripped out that require the write() function to be more complex for some reason. @krzysztof.galazka_intel.com ?

[kgalazka]

In D50127#1144438, @erj wrote:

I'm going to assume there are some hidden #ifdefs that are getting stripped out that require the write() function to be more complex for some reason. @krzysztof.galazka_intel.com ?

I'm looking into that, but it's been a while since I tinkered with X55n, so a lot of cache misses, sorry ;)

Anyway - those functions are also not implemented in Linux and DPDK drivers. In my understanding ixgbe_phy_x550em_kr means that an internal PHY is used, which is configured without using MDIO. For external PHYs connected through KR there is another PHY type: ixgbe_phy_x550em_ext_t. It has it's own set of PHY ops.

@adrian I don't think it's a good idea to add that. At least not without some kind of tunable/sysctl knob, which will be disabled by default.

[adrian]

In D50127#1145007, @krzysztof.galazka_intel.com wrote:

In D50127#1144438, @erj wrote:

I'm going to assume there are some hidden #ifdefs that are getting stripped out that require the write() function to be more complex for some reason. @krzysztof.galazka_intel.com ?

I'm looking into that, but it's been a while since I tinkered with X55n, so a lot of cache misses, sorry ;)

Anyway - those functions are also not implemented in Linux and DPDK drivers. In my understanding ixgbe_phy_x550em_kr means that an internal PHY is used, which is configured without using MDIO. For external PHYs connected through KR there is another PHY type: ixgbe_phy_x550em_ext_t. It has it's own set of PHY ops.

@adrian I don't think it's a good idea to add that. At least not without some kind of tunable/sysctl knob, which will be disabled by default.

oh interesting. yeah I just went and re-checked mainline DPDK and you're right, they're not there. I wonder why it was submitted / landed and then removed at some point? I'll go dig into it some more.

Ok, I'll ignore this diff for now until i get a board that seems to require it for some reason.

[adrian]

abandoning for now; it isn't required for MDIO support, and it may actually be incorrect in almost all cases outside of some specific hardware (which I don't have)