linux-kernel - Re: [PATCH -tip 1/5] add asm-generic/dma-mappig.h

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Date:	Thu, 7 May 2009 12:38:04 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, tony.luck@...el.com,
	linux-ia64@...r.kernel.org
Subject: Re: [PATCH -tip 1/5] add asm-generic/dma-mappig.h

On Thursday 07 May 2009, FUJITA Tomonori wrote:
> This header file provides some generic dma mapping function
> definitions for the users of struct dma_map_ops.
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>

I'm currently trying to add asm-generic variants for all of
the common headers. One of my goals there is to make them
as complete as possible, i.e. if a header file in asm-generic
has the same name as one in any of the architectures, it should
IMHO provide the same (full) API.

I would therefore suggest that you either rename the file to
something like dma-mapping-common.h or add some template
functions that can be overriden per architecture, like

#ifndef dma_get_ops
static inline struct dma_map_ops *get_dma_ops(struct device *dev)
{
	return dma_ops;
}
#endif
#ifndef dma_alloc_coherent
/*
 * to be defined out of line
 */
extern void *dma_alloc_coherent(struct device *dev, size_t size,
		dma_addr_t *dma_handle, gfp_t gfp);
#endif

Then an architecture can opt-in to do things like:

#define dma_get_ops dma_get_ops
static inline struct dma_map_ops *get_dma_ops(struct device *dev)
{
	return dev->archdata.dma_ops;
}

before the #include <asm-generic/dma-mapping.h>

> +static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
> +					      size_t size,
> +					      enum dma_data_direction dir,
> +					      struct dma_attrs *attrs)
> +{
> +	struct dma_map_ops *ops = get_dma_ops(dev);
> +	dma_addr_t addr;
> +
> +	kmemcheck_mark_initialized(ptr, size);
> +	BUG_ON(!valid_dma_direction(dir));
> +	addr = ops->map_page(dev, virt_to_page(ptr),
> +			     (unsigned long)ptr & ~PAGE_MASK, size,
> +			     dir, NULL);
> +	debug_dma_map_page(dev, virt_to_page(ptr),
> +			   (unsigned long)ptr & ~PAGE_MASK, size,
> +			   dir, addr, true);
> +	return addr;
> +}

You are not passing the dma_attrs down here, which I think you need to,
if any of the architectures using this file want to support DMA attributes.

> +
> +static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
> +					  size_t size,
> +					  enum dma_data_direction dir,
> +					  struct dma_attrs *attrs)
> +{
> +	struct dma_map_ops *ops = get_dma_ops(dev);
> +
> +	BUG_ON(!valid_dma_direction(dir));
> +	if (ops->unmap_page)
> +		ops->unmap_page(dev, addr, size, dir, NULL);
> +	debug_dma_unmap_page(dev, addr, size, dir, true);
> +}

same here and in the next few functions.

	Arnd <><
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