[PATCH 4/4] powerpc/mpc8548: Add workaround for erratum NMG_SRIO135

[David Laight]

> Issue:
> Applications using lwarx/stwcx instructions in the core to
> compete for a software lock or semaphore with a device on
> RapidIO using read atomic set, clr, inc, or dec in a similar
> manner may falsely result in both masters seeing the lock
> as "available". This could result in data corruption as
> both masters try to modify the same piece of data protected
> by the lock.
> 
> Workaround:
> Set bits 13 and 29 of CCSR offset 0x01010 (EEBPCR register
> of the ECM) during initialization and leave them set
> indefinitely. This may slightly degrade overall system
> performance.

Might be worth actually saying what these bits do, and
why/when overall performance is affected.

Is the problem trying to do locked read-write cycles
on a slow peripheral bus?
Might be a case for just 'not doing that'.

	David