[PATCH 2/2] phy: armada-38x: fix NETA lockup when repeatedly switching speeds

[Russell King - ARM Linux admin]

On Wed, Jul 01, 2020 at 12:27:27PM +0530, Vinod Koul wrote:
> On 30-06-20, 17:05, Russell King wrote:
> > The mvneta hardware appears to lock up in various random ways when
> > repeatedly switching speeds between 1G and 2.5G, which involves
> > reprogramming the COMPHY.  It is not entirely clear why this happens,
> > but best guess is that reprogramming the COMPHY glitches mvneta clocks
> > causing the hardware to fail.  It seems that rebooting resolves the
> > failure, but not down/up cycling the interface alone.
> > 
> > Various other approaches have been tried, such as trying to cleanly
> > power down the COMPHY and then take it back through the power up
> > initialisation, but this does not seem to help.
> > 
> > It was finally noticed that u-boot's last step when configuring a
> > COMPHY for "SGMII" mode was to poke at a register described as
> > "GBE_CONFIGURATION_REG", which is undocumented in any external
> > documentation.  All that we have is the fact that u-boot sets a bit
> > corresponding to the "SGMII" lane at the end of COMPHY initialisation.
> > 
> > Experimentation shows that if we clear this bit prior to changing the
> > speed, and then set it afterwards, mvneta does not suffer this problem
> > on the SolidRun Clearfog when switching speeds between 1G and 2.5G.
> > 
> > This problem was found while script-testing phylink.
> > 
> > Signed-off-by: Russell King <rmk+kernel at armlinux.org.uk>
> > ---
> >  arch/arm/boot/dts/armada-38x.dtsi          |  3 +-
> 
> lgtm, i need ack for dts parts before I can apply this

I'm not sure what the situation is for Bootlin, but they don't seem to
be very responsive right now (covid related?)

What I know from what I've been party to on netdev is that Bootlin
sent a patch for the MVPP2 driver, and the very next day someone
reported that the patch caused a bug.  Unfortunately, the patch got
picked up anyway, but there was no response from Bootlin.  After a
month or so, -final was released containing this patch, so now it
had become a regression - and still no response from Bootlin.

Eventually the bug got fixed - not because Bootlin fixed it, but
because I ended up spending the time researching how that part of
the network driver worked, diagnosing what was going on, and
eventually fixing it in the most obvious way - but it's not clear
that the fix was the right approach.  Bootlin never commented.  See
3138a07ce219 ("net: mvpp2: fix RX hashing for non-10G ports").

So, I think we have to assume that Bootlin are struggling right now,
and as it's been over a week, it's unlikely that they are going to
respond soon.  What do you think we should do?

I also note that Rob has not responded to the DT binding change
either, despite me gently prodding, and Rob processing a whole raft
of DT binding stuff yesterday.

I can split the DTS change from the rest of the patch, but I don't
think that really helps without at least the binding change being
agreed.

-- 
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