linux-kernel - Re: [PATCH v3] arm/mm/dma-mapping.c: Add arm_coherent_dma

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Date:	Thu, 07 May 2015 17:18:25 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
Cc:	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] arm/mm/dma-mapping.c: Add arm_coherent_dma_mmap

On Thursday 07 May 2015 14:54:17 Mike Looijmans wrote:
> 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@...ic.nl>
> 

Looks good to me

Acked-by: Arnd Bergmann <arnd@...db.de>
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