Re: [PATCH v2 0/3] Fix Armada 38x mvneta lockups when switching speeds

[Vinod Koul <vkoul@kernel.org>]

On 21-07-20, 15:37, Russell King - ARM Linux admin wrote:
> Hi,
> 
> While testing phylink over the weekend, I found it was possible to
> cause the mvneta hardware to lockup in various weird and wonderful
> ways by switching the interface speed between 1G and 2.5G repeatedly.
> It didn't require a rapid switching, but one switch every few seconds.
> 
> Symptoms included one or more of:
> - Timeout while trying to stop transmit (seen once)
> - 2500BASE-X link negotiation failure (fails to exchange link word.)
> - Detects lack of sync, but fails to flag 10ms of sync failure.
> - SyncOk bit randomly toggles.
> 
> Once the hardware gets into a "bad" state, trying to recover it by
> using the mvneta GMAC port reset fails to resolve the issue.
> Disabling the port also fails to recover it.  The only way to
> recover seemed to be via a reboot.
> 
> Many solutions to solve this were tried in various combinations -
> while changing the COMPHY configuration:
> - putting the GMAC into reset
> - disabling the GMAC port
> - augmenting the COMPHY configuration to try to "cleanly" disable
>   the COMPHY via phy_power_down() and reconfigure it via
>   phy_power_up(), including resetting parts of the COMPHY and
>   re-running the RX initialisation.
> 
> None of that worked.  It was then discovered from the u-boot sources
> that there is an undocumented register that has a lane-specific bit
> set at the end of COMPHY initialisation, once the loosely documented
> COMPHY setup has completed.
> 
> Experimentation with that showed that if the lane specific bit is
> cleared before changing the COMPHY "GEN" configuration, and set
> afterwards, mvneta no longer locks up.
> 
> Unfortunately, this undocumented register is not part of the COMPHY
> register set that we map - it is located in a region of "System
> Registers" which are shared between multiple different devices.
> 
> Who should be responsible for mapping this register (mvneta or
> COMPHY) was considered; the register is only present on Armada 38x
> systems, and seemingly not on Armada 37x or Armada 37xx systems.
> It seems that it is a system-level register.  The COMPHYs seem to
> be system specific, so let's make it part of the COMPHY.
> 
> With no real information on this register, all we can do is guess
> about it's function and how to fit it into the system.

Applied 1 & 3, thanks
-- 
~Vinod