[PATCH v2 3/3] phy: armada-38x: fix NETA lockup when repeatedly switching speeds

[Andrew Lunn]

On Tue, Jul 21, 2020 at 03:40:43PM +0100, 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.
> 
> This fix also requires the corresponding change to DT to be effective.
> See "ARM: dts: armada-38x: fix NETA lockup when repeatedly switching
> speeds".
> 
> Fixes: 14dc100b4411 ("phy: armada38x: add common phy support")
> Signed-off-by: Russell King <rmk+kernel at armlinux.org.uk>

Reviewed-by: Andrew Lunn <andrew at lunn.ch>

    Andrew