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Commit 4aa806b7 authored by Russell King's avatar Russell King
Browse files

DMA-API: provide a helper to set both DMA and coherent DMA masks 



Provide a helper to set both the DMA and coherent DMA masks to the
same value - this avoids duplicated code in a number of drivers,
sometimes with buggy error handling, and also allows us identify
which drivers do things differently.

Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 272b98c6

Documentation/DMA-API-HOWTO.txt

+22 −15
Original line number Diff line number Diff line
@@ -101,12 +101,21 @@ style to do this even if your device holds the default setting, 
because this shows that you did think about these issues wrt. your

device.



The query is performed via a call to dma_set_mask():

The query is performed via a call to dma_set_mask_and_coherent():



	int dma_set_mask_and_coherent(struct device *dev, u64 mask);



which will query the mask for both streaming and coherent APIs together.

If you have some special requirements, then the following two separate

queries can be used instead:



	The query for streaming mappings is performed via a call to

	dma_set_mask():



		int dma_set_mask(struct device *dev, u64 mask);



The query for consistent allocations is performed via a call to

dma_set_coherent_mask():

	The query for consistent allocations is performed via a call

	to dma_set_coherent_mask():



		int dma_set_coherent_mask(struct device *dev, u64 mask);
@@ -137,7 +146,7 @@ exactly why. 


The standard 32-bit addressing device would do something like this:



	if (dma_set_mask(dev, DMA_BIT_MASK(32))) {

	if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))) {

		printk(KERN_WARNING

		       "mydev: No suitable DMA available.\n");

		goto ignore_this_device;
@@ -171,22 +180,20 @@ the case would look like this: 


	int using_dac, consistent_using_dac;



	if (!dma_set_mask(dev, DMA_BIT_MASK(64))) {

	if (!dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64))) {

		using_dac = 1;

	   	consistent_using_dac = 1;

		dma_set_coherent_mask(dev, DMA_BIT_MASK(64));

	} else if (!dma_set_mask(dev, DMA_BIT_MASK(32))) {

	} else if (!dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))) {

		using_dac = 0;

		consistent_using_dac = 0;

		dma_set_coherent_mask(dev, DMA_BIT_MASK(32));

	} else {

		printk(KERN_WARNING

		       "mydev: No suitable DMA available.\n");

		goto ignore_this_device;

	}



dma_set_coherent_mask() will always be able to set the same or a

smaller mask as dma_set_mask(). However for the rare case that a

The coherent coherent mask will always be able to set the same or a

smaller mask as the streaming mask. However for the rare case that a

device driver only uses consistent allocations, one would have to

check the return value from dma_set_coherent_mask().
@@ -199,9 +206,9 @@ address you might do something like: 
		goto ignore_this_device;

	}



When dma_set_mask() is successful, and returns zero, the kernel saves

away this mask you have provided.  The kernel will use this

information later when you make DMA mappings.

When dma_set_mask() or dma_set_mask_and_coherent() is successful, and

returns zero, the kernel saves away this mask you have provided.  The

kernel will use this information later when you make DMA mappings.



There is a case which we are aware of at this time, which is worth

mentioning in this documentation.  If your device supports multiple

Documentation/DMA-API.txt

+8 −0
Original line number Diff line number Diff line
@@ -141,6 +141,14 @@ won't change the current mask settings. It is more intended as an 
internal API for use by the platform than an external API for use by

driver writers.



int

dma_set_mask_and_coherent(struct device *dev, u64 mask)



Checks to see if the mask is possible and updates the device

streaming and coherent DMA mask parameters if it is.



Returns: 0 if successful and a negative error if not.



int

dma_set_mask(struct device *dev, u64 mask)

include/linux/dma-mapping.h

+14 −0
Original line number Diff line number Diff line
@@ -97,6 +97,20 @@ static inline int dma_set_coherent_mask(struct device *dev, u64 mask) 
}

#endif



/*

 * Set both the DMA mask and the coherent DMA mask to the same thing.

 * Note that we don't check the return value from dma_set_coherent_mask()

 * as the DMA API guarantees that the coherent DMA mask can be set to

 * the same or smaller than the streaming DMA mask.

 */

static inline int dma_set_mask_and_coherent(struct device *dev, u64 mask)

{

	int rc = dma_set_mask(dev, mask);

	if (rc == 0)

		dma_set_coherent_mask(dev, mask);

	return rc;

}



extern u64 dma_get_required_mask(struct device *dev);



static inline unsigned int dma_get_max_seg_size(struct device *dev)