[OpenWrt-Devel] [RFC v2 6/6] ar71xx: Reset QCA955x SGMII link on speed change

[Sven Eckelmann]

On Tuesday 05 April 2016 15:32:13 Sven Eckelmann wrote:
> From: Sven Eckelmann <sven.eckelmann at open-mesh.com>
> 
> The SGMII link of the QCA955x seems to be unstable when the PHY changes the
> link speed. Reseting the SGMII and the PHY management control seems to
> resolve this problem.
> 
> This was observed with an AR8033 and QCA9558
> 
> Signed-off-by: Sven Eckelmann <sven.eckelmann at open-mesh.com>
> ---
> v2:
>  - Split into multiple patches and adjust slightly to look more like an
>    OpenWrt patch
> 
> The code of this RFC is not meant to be an actual patch. It should show
> what the u-boot for QCA955x does and what seemed to work(tm) in my limited
> tests. It would be interesting to know whether this was also noticed by
> other people and how they fixed it (when they fixed it).

Just because asked if this is also required for the RGMII - short answer:
yes, it is.

Slightly longer answer: Yes, the link seems to desync(?) too when RGMII
changes the link speed. Unfortunately, there is also no real fix and the
workaround is even more terrible. The basic idea behind it is that the PHY has
to be changed into its digital loopback mode on each link change. And then the
SoC has to transfer some ethernet frames to the PHY and check if it receives
these packets again. If not, then it has to toggle the TX_INVERT bit of
ETH_CFG and retest. If it still doesn't work then the only solution for the
SoC is to jump out of the window (this part is not yet implemented).

I have just implemented a PoC in case somebody wants to play around with it.
Not that I would recommend that to anyone.

Kind regards,
	Sven
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