From: FUJITA Tomonori IOMMUs merges scatter/gather segments without considering a low level driver's restrictions. The problem is that IOMMUs can't access to the limitations because they are in request_queue. This patchset introduces a new structure, device_dma_parameters, including dma information. A pointer to device_dma_parameters is added to struct device. The bus specific structures (like pci_dev) includes device_dma_parameters. Low level drivers can use dma_set_max_seg_size to tell IOMMUs about the restrictions. We can move more dma stuff in struct device (like dma_mask) to struct device_dma_parameters later (needs some cleanups before that). This includes patches for all the IOMMUs that could merge sg (x86_64, ppc, IA64, alpha, sparc64, and parisc) though only the ppc patch was tested. The patches for other IOMMUs are only compile tested. This patch: Add a new structure, device_dma_parameters, including dma information. A pointer to device_dma_parameters is added to struct device. - there are only max_segment_size and segment_boundary_mask there but we'll move more dma stuff in struct device (like dma_mask) to struct device_dma_parameters later. segment_boundary_mask is not supported yet. - new accessors for the dma parameters are added. So we can easily change where to place struct device_dma_parameters in the future. - dma_get_max_seg_size returns 64K if dma_parms in struct device isn't set up properly. 64K is the default max_segment_size in the block layer. Signed-off-by: FUJITA Tomonori Acked-by: Jeff Garzik Cc: James Bottomley Cc: Jens Axboe Signed-off-by: Andrew Morton --- include/linux/device.h | 11 +++++++++++ include/linux/dma-mapping.h | 15 +++++++++++++++ 2 files changed, 26 insertions(+) diff -puN include/linux/device.h~iommu-sg-merging-add-device_dma_parameters-structure include/linux/device.h --- a/include/linux/device.h~iommu-sg-merging-add-device_dma_parameters-structure +++ a/include/linux/device.h @@ -392,6 +392,15 @@ extern int devres_release_group(struct d extern void *devm_kzalloc(struct device *dev, size_t size, gfp_t gfp); extern void devm_kfree(struct device *dev, void *p); +struct device_dma_parameters { + /* + * a low level driver may set these to teach IOMMU code about + * sg limitations. + */ + unsigned int max_segment_size; + unsigned long segment_boundary_mask; +}; + struct device { struct klist klist_children; struct klist_node knode_parent; /* node in sibling list */ @@ -427,6 +436,8 @@ struct device { 64 bit addresses for consistent allocations such descriptors. */ + struct device_dma_parameters *dma_parms; + struct list_head dma_pools; /* dma pools (if dma'ble) */ struct dma_coherent_mem *dma_mem; /* internal for coherent mem diff -puN include/linux/dma-mapping.h~iommu-sg-merging-add-device_dma_parameters-structure include/linux/dma-mapping.h --- a/include/linux/dma-mapping.h~iommu-sg-merging-add-device_dma_parameters-structure +++ a/include/linux/dma-mapping.h @@ -60,6 +60,21 @@ static inline int is_device_dma_capable( extern u64 dma_get_required_mask(struct device *dev); +static inline unsigned int dma_get_max_seg_size(struct device *dev) +{ + return dev->dma_parms ? dev->dma_parms->max_segment_size : 65536; +} + +static inline unsigned int dma_set_max_seg_size(struct device *dev, + unsigned int size) +{ + if (dev->dma_parms) { + dev->dma_parms->max_segment_size = size; + return 0; + } else + return -EIO; +} + /* flags for the coherent memory api */ #define DMA_MEMORY_MAP 0x01 #define DMA_MEMORY_IO 0x02 _