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

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Date:	Thu, 7 May 2015 14:07:25 +0200
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	<linux-arm-kernel@...ts.infradead.org>
CC:	<arnd@...db.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm/mm/dma-mapping.c: Add arm_coherent_dma_mmap

Oops, "arch/arm/boot/dts/topic-dyplo.dtsi" should not have been in there. Will 
send a v2 patch to correct that.

On 07-05-15 14:00, 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>
> ---
>   arch/arm/boot/dts/topic-dyplo.dtsi |  1 +
>   arch/arm/mm/dma-mapping.c          | 32 +++++++++++++++++++++++++-------
>   2 files changed, 26 insertions(+), 7 deletions(-)



Kind regards,

Mike Looijmans
System Expert

TOPIC Embedded Products
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