Fix for direct attach cable and workaround for intermittent link issue with axgbe

[rajesh1.kumar_amd.com]

Summary

This patch has fixes for link related issues with axgbe driver

Intermittently, some link issues observed with axgbe driver. By default,
axgbe driver does a receiver reset after predefined number of retries for the
link to come up. But intermittently, this receiver reset doesn't suffice.
In that case, as a workaround we need to reset the phy completely.

This patch introduces a sysctl where which can be set to reset the phy
completely, rather than just doing receiver reset.

This patch also has the necessary fixes for handling the direct attach cables
properly.

Test Plan

When trying with axgbe driver, if link doesn't comeup, the following sysctl
can be set as below.

Enable link workaround
dev.ax.X.link_workaround=1

[vmaffione]

Wouldn't it be easier to always perform the complete phy reset if this is a known hardware issue? Or maye perform it automatically after a normal reset does not work?
I'm afraid that adding an obscure sysctl (obscure for anyone except for the axgbe developers) would be of little use. Unaware users wouldn't have a clue about what to do...
just my 2 cents

[rajesh1.kumar_amd.com]

In D28266#632505, @vmaffione wrote:

Wouldn't it be easier to always perform the complete phy reset if this is a known hardware issue? Or maye perform it automatically after a normal reset does not work?
I'm afraid that adding an obscure sysctl (obscure for anyone except for the axgbe developers) would be of little use. Unaware users wouldn't have a clue about what to do...
just my 2 cents

Thanks for your inputs @vmaffione. Resetting the receiver side is sufficient and supposed to recognize the link as per the spec. That is why the earlier code just do the receiver reset. But since it fails intermittently, we reset the complete phy as a workaround (not a fix) to get around this issue. We are internally working on this issue. Once a final resolution is arrived, this workaround can be removed.

For now, Once this patch is accepted, I will update the man page for the driver (D27800) with this sysctl for the users to be aware of it. Please let me know your comments.

[rajesh1.kumar_amd.com]

Any more comments on this patch?

[vmaffione]

Will the fix be provided as a firmware upgrade or how?
I could commit this change if you don't have someone else around that can do that for you.

[rajesh1.kumar_amd.com]

In D28266#633046, @vmaffione wrote:

Will the fix be provided as a firmware upgrade or how?
I could commit this change if you don't have someone else around that can do that for you.

Yes @vmaffione, the permanent fix would be most likely a BIOS update.

I don't have push access to the gerrit repo. So, it would be helpful if you can push these changes. I will update the man page once it's accepted. Thanks for all your inputs and time.

[rajesh1.kumar_amd.com]

Thanks @vmaffione for pushing it upstream.

[rajesh1.kumar_amd.com]

@vmaffione, Sorry I just noticed that the stable/13 branch is created yesterday. So, can this patch be pushed to that branch as well? or do I need to submit the same patch separately for stable/13 branch?

[vmaffione]

It can be merged there (MFC'd) as well, after a period of a minimum of 3 days. There is no need to submit a separate patch.

[rajesh1.kumar_amd.com]

It can be merged there (MFC'd) as well, after a period of a minimum of 3 days. There is no need to submit a separate patch.

That would be great. Thanks for the update @vmaffione