Re: [PATCH] net: stmmac: dwmac-imx: pause the TXC clock in fixed-link

[Vladimir Oltean <olteanv@gmail.com>]

Hi Andrew,

On Wed, Jul 26, 2023 at 10:32:00AM +0200, Andrew Lunn wrote:
> On Tue, Jul 25, 2023 at 02:49:31PM -0500, Shenwei Wang wrote:
> > When using a fixed-link setup, certain devices like the SJA1105 require a
> > small pause in the TXC clock line to enable their internal tunable
> > delay line (TDL).
> 
> The SJA1105 has the problem, so i would expect it to be involved in
> the solution. Otherwise, how is this going to work for other MAC
> drivers?
> 
> Maybe you need to expose a common clock framework clock for the TXC
> clock line, which the SJA1105 can disable/enable? That then makes it
> clear what other MAC drivers need to do.
> 
>       Andrew
> 

The delicate nature of the SJA1105 bug is that as far as I understand,
the switch is not aware of the fact that its RGMII delay line went out
of whack. Its port MII status registers say that they're okay.

Also, if I understand Shenwei's workaround procedure, it deals more with
"prevention" than with "recovery". I'm not sure that (reliable) recovery
is possible. I'm trying to gather more data from NXP colleagues.