RE: [PATCH net 1/2] dt: ar803x: Document disable-hibernation property

[Wei Fang]

> -----Original Message-----
> From: Andrew Lunn <andrew@xxxxxxx>
> Sent: 2022年8月18日 9:20
> To: Wei Fang <wei.fang@xxxxxxx>
> Cc: hkallweit1@xxxxxxxxx; linux@xxxxxxxxxxxxxxx; davem@xxxxxxxxxxxxx;
> edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx;
> robh+dt@xxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx; f.fainelli@xxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH net 1/2] dt: ar803x: Document disable-hibernation
> property
> 
> > Hi Andrew,
> >
> > 	Your suggestion is indeed an effective solution, but I checked both
> > the datasheet and the driver of AR803x PHYs and found that the
> > qca,clk-out-frequency and the qca,keep-pll-enabled properties are associated
> with the CLK_25M pin of AR803x PHYs.
> > But there is a case that CLK_25M pin is not used on some platforms.
> > Taking our i.MX8DXL platform as an example, the stmmac and AR8031 PHY
> > are applied on this platform, but the CLK_25M pin of AR8031 is not
> > used. So when I used the method you mentioned above, it did not work
> > as expected. In this case, we can only disable the hibernation mode of
> > AR803x PHYs and keep the RX_CLK always outputting a valid clock so that the
> stmmac can complete the software reset operation.
> 
> What happens to the RX_CLK when you unplug the cable? It is no longer
> receiving anything, so i would expect the RX_CLK to stop ticking. Does that
> cause problems for the MAC?
> 
Yes, after the PHY enters hibernation mode that the RX_CLK stop ticking, but
for stmmac, it is essential that RX_CLK of PHY is present for software reset
completion. Otherwise, the stmmac is failed to complete the software reset
and can not init DMA.

>      Andrew