Date:	Mon, 1 Jun 2009 13:02:42 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	arnd@...db.de
Cc:	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] asm-generic: add dma-mapping-linear.h

On Thu, 28 May 2009 21:04:55 +0100
Arnd Bergmann <arnd@...db.de> wrote:

> This adds a version of the dma-mapping API to asm-generic that can be
> used by most architectures that only need a linear mapping.
> 
> An architecture using this still needs to provide definitions for
> dma_get_cache_alignment, dma_cache_sync and a new dma_coherent_dev
> function as well as out-of-line versions of dma_alloc_coherent and
> dma_free_coherent.
> 
> Thanks to Fujita-san for an endless supply of feedback.
> 
> Cc: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> ---
>  include/asm-generic/dma-mapping-linear.h |  336 ++++++++++++++++++++++++++++++
>  1 files changed, 336 insertions(+), 0 deletions(-)
>  create mode 100644 include/asm-generic/dma-mapping-linear.h
> 
> ---
> 
> I've added this version to
> git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic#next
> 
> I also have patches to convert the existing architectures to use
> it, but I plan to submit those to the arch maintainers once asm-generic
> series has been merged.

IMO, this need to be merged with some users. We don't want to merge
something that nobody wants to use.


> Please ack if you are happy with this version.
> 
> diff --git a/include/asm-generic/dma-mapping-linear.h b/include/asm-generic/dma-mapping-linear.h
> new file mode 100644
> index 0000000..c3b987d
> --- /dev/null
> +++ b/include/asm-generic/dma-mapping-linear.h
> @@ -0,0 +1,336 @@
> +#ifndef __ASM_GENERIC_DMA_MAPPING_H
> +#define __ASM_GENERIC_DMA_MAPPING_H
> +
> +#include <linux/mm.h>
> +#include <linux/device.h>
> +#include <linux/dma-debug.h>
> +#include <linux/scatterlist.h>
> +#include <asm/cacheflush.h>
> +#include <asm/io.h>
> +
> +/**
> + * dma_alloc_coherent - allocate consistent memory for DMA
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @size: required memory size
> + * @handle: bus-specific DMA address
> + *
> + * Allocate some uncached, unbuffered memory for a device for
> + * performing DMA.  This function allocates pages, and will
> + * return the CPU-viewed address, and sets @handle to be the
> + * device-viewed address.
> + */
> +extern void *
> +dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
> +		   gfp_t flag);
> +
> +/**
> + * dma_free_coherent - free memory allocated by dma_alloc_coherent
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @size: size of memory originally requested in dma_alloc_coherent
> + * @cpu_addr: CPU-view address returned from dma_alloc_coherent
> + * @handle: device-view address returned from dma_alloc_coherent
> + *
> + * Free (and unmap) a DMA buffer previously allocated by
> + * dma_alloc_coherent().
> + *
> + * References to memory and mappings associated with cpu_addr/handle
> + * during and after this call executing are illegal.
> + */
> +extern void
> +dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
> +		  dma_addr_t dma_handle);
> +
> +#define dma_alloc_noncoherent(d, s, h, f) dma_alloc_coherent(d, s, h, f)
> +#define dma_free_noncoherent(d, s, v, h) dma_free_coherent(d, s, v, h)
> +
> +/**
> + * dma_map_single - map a single buffer for streaming DMA
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @cpu_addr: CPU direct mapped address of buffer
> + * @size: size of buffer to map
> + * @dir: DMA transfer direction
> + *
> + * Ensure that any data held in the cache is appropriately discarded
> + * or written back.
> + *
> + * The device owns this memory once this call has completed.  The CPU
> + * can regain ownership by calling dma_unmap_single() or dma_sync_single().
> + */
> +static inline dma_addr_t
> +dma_map_single(struct device *dev, void *ptr, size_t size,
> +	       enum dma_data_direction direction)
> +{
> +	dma_addr_t dma_addr = virt_to_bus(ptr);
> +	BUG_ON(!valid_dma_direction(direction));
> +
> +	if (!dma_coherent_dev(dev))
> +		dma_cache_sync(dev, ptr, size, direction);

Where can I find dma_coherent_dev?

I don't fancy this since this is architecture-specific stuff (not
generic things).


> +	debug_dma_map_page(dev, virt_to_page(ptr),
> +			   (unsigned long)ptr & ~PAGE_MASK, size,
> +			   direction, dma_addr, true);
> +
> +	return dma_addr;
> +}
> +
> +/**
> + * dma_unmap_single - unmap a single buffer previously mapped
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @handle: DMA address of buffer
> + * @size: size of buffer to map
> + * @dir: DMA transfer direction
> + *
> + * Unmap a single streaming mode DMA translation.  The handle and size
> + * must match what was provided in the previous dma_map_single() call.
> + * All other usages are undefined.
> + *
> + * After this call, reads by the CPU to the buffer are guaranteed to see
> + * whatever the device wrote there.
> + */
> +static inline void
> +dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
> +		 enum dma_data_direction direction)
> +{
> +	debug_dma_unmap_page(dev, dma_addr, size, direction, true);
> +}
> +
> +/**
> + * dma_map_sg - map a set of SG buffers for streaming mode DMA
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @sg: list of buffers
> + * @nents: number of buffers to map
> + * @dir: DMA transfer direction
> + *
> + * Map a set of buffers described by scatterlist in streaming
> + * mode for DMA.  This is the scatter-gather version of the
> + * above pci_map_single interface.  Here the scatter gather list
> + * elements are each tagged with the appropriate dma address
> + * and length.  They are obtained via sg_dma_{address,length}(SG).
> + *
> + * NOTE: An implementation may be able to use a smaller number of
> + *       DMA address/length pairs than there are SG table elements.
> + *       (for example via virtual mapping capabilities)
> + *       The routine returns the number of addr/length pairs actually
> + *       used, at most nents.
> + *
> + * Device ownership issues as mentioned above for pci_map_single are
> + * the same here.
> + */
> +static inline int
> +dma_map_sg(struct device *dev, struct scatterlist *sglist, int nents,
> +	   enum dma_data_direction direction)
> +{
> +	struct scatterlist *sg;
> +	int i, sync;
> +
> +	BUG_ON(!valid_dma_direction(direction));
> +	WARN_ON(nents == 0 || sglist[0].length == 0);
> +
> +	sync = !dma_coherent_dev(dev);
> +
> +	for_each_sg(sglist, sg, nents, i) {
> +		BUG_ON(!sg_page(sg));
> +
> +		sg->dma_address = page_to_bus(sg_page(sg)) + sg->offset;
> +		sg_dma_len(sg) = sg->length;
> +		if (sync)
> +			dma_cache_sync(dev, sg_virt(sg), sg->length, direction);
> +	}
> +
> +	debug_dma_map_sg(dev, sg, nents, i, direction);
> +
> +	return nents;
> +}
> +
> +/**
> + * dma_unmap_sg - unmap a set of SG buffers mapped by dma_map_sg
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @sg: list of buffers
> + * @nents: number of buffers to map
> + * @dir: DMA transfer direction
> + *
> + * Unmap a set of streaming mode DMA translations.
> + * Again, CPU read rules concerning calls here are the same as for
> + * pci_unmap_single() above.
> + */
> +static inline void
> +dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nhwentries,
> +	     enum dma_data_direction direction)
> +{
> +	debug_dma_unmap_sg(dev, sg, nhwentries, direction);
> +}
> +
> +/**
> + * dma_map_page - map a portion of a page for streaming DMA
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @page: page that buffer resides in
> + * @offset: offset into page for start of buffer
> + * @size: size of buffer to map
> + * @dir: DMA transfer direction
> + *
> + * Ensure that any data held in the cache is appropriately discarded
> + * or written back.
> + *
> + * The device owns this memory once this call has completed.  The CPU
> + * can regain ownership by calling dma_unmap_page() or dma_sync_single().
> + */
> +static inline dma_addr_t
> +dma_map_page(struct device *dev, struct page *page, unsigned long offset,
> +	     size_t size, enum dma_data_direction direction)
> +{
> +	return dma_map_single(dev, page_address(page) + offset,
> +			      size, direction);
> +}
> +
> +/**
> + * dma_unmap_page - unmap a buffer previously mapped through dma_map_page()
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @handle: DMA address of buffer
> + * @size: size of buffer to map
> + * @dir: DMA transfer direction
> + *
> + * Unmap a single streaming mode DMA translation.  The handle and size
> + * must match what was provided in the previous dma_map_single() call.
> + * All other usages are undefined.
> + *
> + * After this call, reads by the CPU to the buffer are guaranteed to see
> + * whatever the device wrote there.
> + */
> +static inline void
> +dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
> +	       enum dma_data_direction direction)
> +{
> +	dma_unmap_single(dev, dma_address, size, direction);
> +}
> +
> +/**
> + * dma_sync_single_for_cpu
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @handle: DMA address of buffer
> + * @size: size of buffer to map
> + * @dir: DMA transfer direction
> + *
> + * Make physical memory consistent for a single streaming mode DMA
> + * translation after a transfer.
> + *
> + * If you perform a dma_map_single() but wish to interrogate the
> + * buffer using the cpu, yet do not wish to teardown the DMA mapping,
> + * you must call this function before doing so.  At the next point you
> + * give the DMA address back to the card, you must first perform a
> + * dma_sync_single_for_device, and then the device again owns the
> + * buffer.
> + */
> +static inline void
> +dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
> +			enum dma_data_direction direction)
> +{
> +	debug_dma_sync_single_for_cpu(dev, dma_handle, size, direction);
> +}
> +
> +static inline void
> +dma_sync_single_range_for_cpu(struct device *dev, dma_addr_t dma_handle,
> +			      unsigned long offset, size_t size,
> +			      enum dma_data_direction direction)
> +{
> +	debug_dma_sync_single_range_for_cpu(dev, dma_handle,
> +					    offset, size, direction);
> +}

This looks wrong. You put dma_coherent_dev hook in sync_*_for_device
but why you don't need it sync_*_for_cpu. It's architecture
specific. Some need both, some need either, and some need nothing.


> +/**
> + * dma_sync_sg_for_cpu
> + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> + * @sg: list of buffers
> + * @nents: number of buffers to map
> + * @dir: DMA transfer direction
> + *
> + * Make physical memory consistent for a set of streaming
> + * mode DMA translations after a transfer.
> + *
> + * The same as dma_sync_single_for_* but for a scatter-gather list,
> + * same rules and usage.
> + */
> +static inline void
> +dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nents,
> +		    enum dma_data_direction direction)
> +{
> +	debug_dma_sync_sg_for_cpu(dev, sg, nents, direction);
> +}
> +
> +static inline void
> +dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle,
> +			   size_t size, enum dma_data_direction direction)
> +{
> +	if (!dma_coherent_dev(dev))
> +		dma_cache_sync(dev, bus_to_virt(dma_handle), size, direction);
> +	debug_dma_sync_single_for_device(dev, dma_handle, size, direction);
> +}
> +
> +static inline void
> +dma_sync_single_range_for_device(struct device *dev, dma_addr_t dma_handle,
> +				 unsigned long offset, size_t size,
> +				 enum dma_data_direction direction)
> +{
> +	if (!dma_coherent_dev(dev))
> +		dma_cache_sync(dev, bus_to_virt(dma_handle), size, direction);
> +	debug_dma_sync_single_range_for_device(dev, dma_handle,
> +					       offset, size, direction);
> +}
> +
> +static inline void
> +dma_sync_sg_for_device(struct device *dev, struct scatterlist *sglist,
> +		       int nents, enum dma_data_direction direction)
> +{
> +	struct scatterlist *sg;
> +	int i;
> +
> +	if (!dma_coherent_dev(dev))
> +		for_each_sg(sglist, sg, nents, i)
> +			dma_cache_sync(dev, sg_virt(sg), sg->length, direction);
> +
> +	debug_dma_sync_sg_for_device(dev, sg, nents, direction);
> +}
> +
> +static inline int
> +dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
> +{
> +	return 0;
> +}
> +
> +/*
> + * Return whether the given device DMA address mask can be supported
> + * properly.  For example, if your device can only drive the low 24-bits
> + * during bus mastering, then you would pass 0x00ffffff as the mask
> + * to this function.
> + */
> +static inline int
> +dma_supported(struct device *dev, u64 mask)
> +{
> +	/*
> +	 * we fall back to GFP_DMA when the mask isn't all 1s,
> +	 * so we can't guarantee allocations that must be
> +	 * within a tighter range than GFP_DMA.
> +	 */
> +	if (mask < 0x00ffffff)
> +		return 0;

I think that this is pretty architecture specific.


> +
> +	return 1;
> +}
> +
> +static inline int
> +dma_set_mask(struct device *dev, u64 dma_mask)
> +{
> +	if (!dev->dma_mask || !dma_supported(dev, dma_mask))
> +		return -EIO;
> +
> +	*dev->dma_mask = dma_mask;
> +
> +	return 0;
> +}
> +
> +static inline int
> +dma_is_consistent(struct device *dev, dma_addr_t dma_addr)
> +{
> +	return dma_coherent_dev(dev);
> +}
> +
> +#endif /* __ASM_GENERIC_DMA_MAPPING_H */
> -- 
> 1.6.3.1
> 
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