linux-kernel - Re: [patch 27/36] Hexagon: Provide DMA implementation

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Message-ID: <16233560.LW8Ali0bj4@wuerfel>
Date:	Wed, 17 Aug 2011 22:01:07 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Richard Kuo <rkuo@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, linux-hexagon@...r.kernel.org,
	Linas Vepstas <linas@...eaurora.org>
Subject: Re: [patch 27/36] Hexagon: Provide DMA implementation

On Wednesday 17 August 2011 11:35:24 Richard Kuo wrote:

> +static dma_addr_t hexagon_map_page(struct device *dev, struct page *page,
> +				   unsigned long offset, size_t size,
> +				   enum dma_data_direction dir,
> +				   struct dma_attrs *attrs)
> +{
> +	dma_addr_t bus = page_to_phys(page) + offset;
> +	WARN_ON(size == 0);
> +
> +	if (!check_addr("map_single", dev, bus, size))
> +		return bad_dma_address;
> +
> +	flush_dcache_range(PAGE_OFFSET + bus, PAGE_OFFSET + bus + size);
> +
> +	return bus;
> +}
> +
> +static void hexagon_sync_single_for_cpu(struct device *dev,
> +					dma_addr_t dma_handle, size_t size,
> +					enum dma_data_direction dir)
> +{
> +	mb();
> +}

Why do you need to flush the cache in map_page, but not in sync?
Normally when you have non-coherent DMA, you need to invalidate
the cache in sync_*_foc_cpu and flush it sync_*_for_device.

	Arnd
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