linux-kernel - Re: [PATCH v2 14/31] arm64: DMA mapping API

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Message-Id: <201208151616.01114.arnd@arndb.de>
Date:	Wed, 15 Aug 2012 16:16:00 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 14/31] arm64: DMA mapping API

On Tuesday 14 August 2012, Catalin Marinas wrote:
> +static struct dma_map_ops arm64_swiotlb_dma_ops = {
> +       .alloc = arm64_swiotlb_alloc_coherent,
> +       .free = arm64_swiotlb_free_coherent,
> +       .map_page = arm64_swiotlb_map_page,
> +       .unmap_page = arm64_swiotlb_unmap_page,
> +       .map_sg = arm64_swiotlb_map_sg_attrs,
> +       .unmap_sg = arm64_swiotlb_unmap_sg_attrs,
> +       .sync_single_for_cpu = arm64_swiotlb_sync_single_for_cpu,
> +       .sync_single_for_device = arm64_swiotlb_sync_single_for_device,
> +       .sync_sg_for_cpu = arm64_swiotlb_sync_sg_for_cpu,
> +       .sync_sg_for_device = arm64_swiotlb_sync_sg_for_device,
> +       .dma_supported = swiotlb_dma_supported,
> +       .mapping_error = swiotlb_dma_mapping_error,
> +};
> +
> +void __init swiotlb_init_with_default_size(size_t default_size, int verbose);
> +
> +void __init arm64_swiotlb_init(size_t max_size)
> +{
> +       dma_ops = &arm64_swiotlb_dma_ops;
> +       swiotlb_init_with_default_size(min((size_t)SZ_64M, max_size), 1);
> +}

Why is swiotlb the default? I would expect that most devices can in fact
use the entire 64 bit address space, so you can use a simple linear
implementation for those.

	Arnd
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