[PATCH v2] realtek: do not reset SerDes on link change

[Birger Koblitz]

Thanks a lot Sander, helpful and efficient!

Cheers,
  Birger

On 11.05.22 22:26, Sander Vanheule wrote:
> Hi Birger,
> 
> On Sun, 2022-05-08 at 16:53 +0200, Birger Koblitz wrote:
>> Hi,
>>
>> On 08.05.22 13:11, Sander Vanheule wrote:
>>> Hi,
>>>
>>> Sorry I didn't get back to this any sooner.
>>>
>>> On Wed, 2022-04-27 at 20:16 +0200, Birger Koblitz wrote:
>>>> Hi,
>>> It's still not clear to me what issue or issues you are fixing exactly with this patch,
>>> and in what way.
>> The patch fixes a bug that was introduced during the merging of the Zyxel XGS1250 code which
>> also is an issue for the XGS1210. The problem as stated with the submitted patch is that
>> a reset of the SerDes connecting to the 8 1GBit ports was done. This is a single XGMII link to
>> the RTL8218D, which provides 8 1GBit ports via this link.
>>
>> The handling of (US)XGMII links is entirely different from the handling of SGMII/HiSGMII, 1000BX
>> or 10GR with a completely different code-path on both the RTL9300 and the RTL9310. The difference
>> is that the internal SerDes is in fact turned "off" in the latter case, and in the former it
>> is put into a suitable XGMII mode. For (Hi)SGMII/1000BX/10GR the SerDes is then put (in its
>> outside "off" state") into what is on RTL931x a suitable "fibre" mode and on RTL9300 into a
>> "forced" mode. All these modes then need to be suitably RX calibrated and the pre- main and post-
>> amplifiers set up properly for TX.
>>
>> The bug was to do a complete SerDes reset on all SerDes links, although the code for setting
>> up the XGMII link was not there, thereby wiping the (RX/TX) setup done by u-boot and breaking the
>> 8 1GBit ports. The 10GBit SFP+ links are mostly understood (from the Ubiquiti USW switch),
>> so here we use the appropriate setup code, which e.g. is necessary when someone pulls a module
>> out and puts another in.
>>
>>>
>>> Is the suggested change in behaviour required for SFP+ modules to completely fix bringing
>>> up new links? Or is this only part of the solution? Your reply makes me think it's the
>> It is only part of the solution. It makes swapping out 10GBit (fiber!) modules possible.
>> It does not allow any 1GBit modules.
> 
> 
> Thanks, this is what I wanted to know! I've rewritten the commit message for this patch to contain
> this info, and pushed it to master.
> 
> Best,
> Sander
>