[PATCH 06/10] soc/qbman: Add ARM equivalent for flush_dcache_range()

[arnd@arndb.de (Arnd Bergmann)]

On Monday, January 23, 2017 7:24:59 PM CET Roy Pledge wrote:
> > Is there a non-"under the covers" way to say "flush this region" without
> > the arch second-guessing whether it really needs to be flushed?
> Any advice on how to resolve this? I looked into trying to do a
> non-cacheable mapping of the
> memory so that the flush wouldn't be required but the ioremap code
> prevents mapping normal
> memory in this way.  The QMan device requiresthis memory to be zeroed at
> startup. Because the device
> does non coherent reads and writes to the memory we must ensure that any
> cache in the CPU cluster(s)
> is flushed in order to prevent a future castout from overwriting data.
> This happened before on PPC
> platforms and made for some very unfun debug session trying to
> understand what was causing the failure.

If this is normal RAM, you should be able to just write zeroes, and then
do a dma_map_single() for initialization. Are there any other requirements
what to do with the memory later, is it used for communication at all,
or just required to be zero?

	Arnd