Acceleration for map_copy_from on powerpc 512x

Fortini Matteo matteo.fortini at
Mon Oct 19 18:52:13 EST 2009

I'm working on a powerpc (PPC512x) embedded Linux product, and while I 
was trying to improve boot time, I found I could exploit the hw in order 
to speed up reading from NOR flashes.
The Linux/mtd version we're using is patches.
Basically, I needed to hack the map_copy_from, which for my arch and 
uncached areas translates to a memcpy, in order to use the SCLPC FIFO, 
with a performance benefit of >2x on aligned multiple of 32Bytes transfers.

I didn't find a cleaner way than just #ifdef'ing the map_copy_from call 
and substitute with my call on relevant cases. I wonder if there is a 
cleaner way.

And yes, as soon as I've cleaned up the code a little bit, I will 
definitely post a patch about it.

Moreover: a huge benefit would come from exploiting DMA on these 
transfers, but I found I'm in_atomic while doing map_copy_from... is 
there an alternative way of locking than just disabling preemption?
I know maybe a newer kernel has already fixed it, but we're kind of 
stuck with the old one since we don't have time to port all of our 
device drivers to 2.6.3x


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