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

[Vinod Koul]

On 10-07-20, 16:19, Russell King - ARM Linux admin wrote:
> 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.

I would prefer splitting, you may sent the DTS to arm arch folks if no
response from subarch folks

-- 
~Vinod