diff options
| -rw-r--r-- | Documentation/DMA-API-HOWTO.txt | 37 | ||||
| -rw-r--r-- | Documentation/DMA-API.txt | 8 | ||||
| -rw-r--r-- | include/linux/dma-mapping.h | 14 |
3 files changed, 44 insertions, 15 deletions
diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt index 14129f1..5e98303 100644 --- a/Documentation/DMA-API-HOWTO.txt +++ b/Documentation/DMA-API-HOWTO.txt @@ -101,14 +101,23 @@ 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(struct device *dev, u64 mask); + int dma_set_mask_and_coherent(struct device *dev, u64 mask); -The query for consistent allocations is performed via a call to -dma_set_coherent_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: - int dma_set_coherent_mask(struct device *dev, u64 mask); + 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(): + + int dma_set_coherent_mask(struct device *dev, u64 mask); Here, dev is a pointer to the device struct of your device, and mask is a bit mask describing which bits of an address your device @@ -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 diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index 78a6c56..e865279 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -142,6 +142,14 @@ 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) Checks to see if the mask is possible and updates the device diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 3a8d0a2..ec951f9 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -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) |
