ARM: 8387/1: arm/mm/dma-mapping.c: Add arm_coherent_dma_mmap

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When dma-coherent transfers are enabled, the mmap call must
not change the pg_prot flags in the vma struct.

Split the arm_dma_mmap into a common and specific parts,
and add a "arm_coherent_dma_mmap" implementation that does
not alter the page protection flags.

Tested on a topic-miami board (Zynq) using the ACP port
to transfer data between FPGA and CPU using the Dyplo
framework. Without this patch, byte-wise access to mmapped
coherent DMA memory was about 20x slower because of the
memory being marked as non-cacheable, and transfer speeds
would not exceed 240MB/s.

After this patch, the mapped memory is cacheable and the
transfer speed is again 600MB/s (limited by the FPGA) when
the data is in the L2 cache, while data integrity is being
maintained.

The patch has no effect on non-coherent DMA.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

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Mike Looijmans 2015-06-03 11:25:31 +01:00 • committed by Russell King

parent e001bbae71

commit 55af8a9164

1 changed files with 25 additions and 7 deletions

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arch/arm/mm/dma-mapping.c

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