[PATCH] ipq806x: dwmac: fix GMACs connected via SGMII fixed-link

[Ansuel Smith]

> fa731838c524 cleared the forced speed in the QSGMII PCS_ALL_CH_CTL
> register during probe, but this is only correct for GMACs that are not
> configured with fixed-link. This prevented GMACs configured with both
> phy-mode = "sgmii" and fixed-link from working properly, as discussed at
> https://github.com/openwrt/openwrt/pull/3954#issuecomment-834625090 and
> the comments that follow. Notably, this prevented all communication
> between gmac2 and the switch on the Netgear R7800.
>
> The correct behavior is to set the QSGMII PCS_ALL_CH_CTL register by
> considering the gmac's fixed-link child, setting the speed as directed by
> fixed-link if present, and otherwise clearing it as was done previously.
>
> Fixes: fa731838c524 ("ipq806x: dwmac: clear forced speed during probe")
> Signed-off-by: Mark Mentovai <mark at moxienet.com>
> Tested-by: Hannu Nyman <hannu.nyman at iki.fi>
> Run-tested: ipq806x/ubnt,unifi-ac-hd, ipq806x/netgear,r7800
> Cc: Petr Štetiar <ynezz at true.cz>
> Cc: Ansuel Smith <ansuelsmth at gmail.com>
> ---
>  ...-dwmac-ipq806x-qsgmii-pcs-all-ch-ctl.patch | 62 +++++++++++++++++--
>  1 file changed, 56 insertions(+), 6 deletions(-)
>

Tested-by:  Ansuel Smith <ansuelsmth at gmail.com>
I also tested this with the qca8k driver on 5.10. Also can you include
this with kernel 5.10
The patch applies without changes also for that kernel.