Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6b7b651055221127304a4e373ee9b762398d54d7
Commit:     6b7b651055221127304a4e373ee9b762398d54d7
Parent:     7bbdc3d51cf793dd81c38f794f4cb73df58d1527
Author:     FUJITA Tomonori <[EMAIL PROTECTED]>
AuthorDate: Mon Feb 4 22:27:55 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Tue Feb 5 09:44:10 2008 -0800

    iommu sg merging: add device_dma_parameters structure
    
    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 <[EMAIL PROTECTED]>
    Acked-by: Jeff Garzik <[EMAIL PROTECTED]>
    Cc: James Bottomley <[EMAIL PROTECTED]>
    Acked-by: Jens Axboe <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 include/linux/device.h      |   11 +++++++++++
 include/linux/dma-mapping.h |   15 +++++++++++++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/include/linux/device.h b/include/linux/device.h
index 479c0b3..2258d89 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -410,6 +410,15 @@ extern int devres_release_group(struct device *dev, void 
*id);
 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 */
@@ -445,6 +454,8 @@ 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 --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4470950..df3a361 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -60,6 +60,21 @@ static inline int is_device_dma_capable(struct device *dev)
 
 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
-
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