[U-Boot] armv7 DMA and cache mangement functions

[Markus Niebel <list-09_u-boot@tqsc.de>]

just a friendly ping:

Am 24.08.2015 um 09:54 schrieb Markus Niebel:
> Hello,
> 
> I'm not an expert in the low level details of this area. So please sorry if there are
> wrong assumptions in this post post.
> 
> Hardware: i.MX6 Solo (TQMa6 on custom Mainboard)
> U-Boot: 2014.10
> gcc: 4.8.3 
> 
> We see an error using TFTP on i.MX6 that seems to triggered, if the code / data size goes
> over a limit. Code changes have nothing to do with network stack, network drivers, 
> memory mangement. TFTP will completely unusable: device sees frequently erroneous packages 
> with different of wierd errors. If code stays below this size all works fine.
> 
> Up to now we checked a lot of things. The following brought us to the assumption, that this
> could be cache related:
> 
> dynamically disable data cache before doing TFTP: 	TFTP works well again
> running with disabled L2 cache (data cache enabled):	TFTP works well again
> 
> Looking at the code in drivers/net/fec_mxc.c, function fec_recv we see a call to
> invalidate_dcache_range before accessing the received ethernet data. When looking at
> the code for invalidate_dcache_range in arch/arm/cpu/armv7/cache_v7.c an comparing
> how the things done in linux and barebox we noticed that the order of L2 chache / data cache
> invalidation is just swapped there. Applying this to the receive code for fec_mxc,
> TFTP will work again.
> 
> Question: is the order of cache invalidation important?
> 
> Thanks
> 
> Markus
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