Hi,
I have a driver where I do memory to memory DMA between GPMC and SDRAM.
Adding a read function, I found that copy_to_user from a
dma_alloc_coherent buffer is significantly slower than from a kmalloc'd one.
Looking at arch/arm/include/asm/pgtable.h I suspect this difference in
speed is due to the fact that the dma_alloc_coherent buffer is unbuffered.
What are my options (besides using mmap)?
* Reserve a portion of memory at boot time to be used as the DMA
destination buffer, use ioremap_cached + manual cache flush as needed?
* Turn on buffering for the DMA destination buffer for the duration of
the copy_to_user call, then turn it off again (and flush it from the cache)?
* Something else entirely?
This is on a 3730, on Linux 2.6.32.
Thanks,
Orjan
--
Orjan Friberg
FlatFrog Laboratories AB
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