[PATCH] arch/microblaze: Added sync method support for DMA and made refinements

[Eli Billauer <eli@billauer.co.il>]

Hi,


This was supposed to be a small patch, but as I dug in, I found that 
several things needed fixing. The sync support was tested by using a 
hardware driver which calls these methods extensively. Scatter-gather 
methods remain completely untested. General DMA operations work, or the 
system would crash, I suppose.


Here's a summary of the changes:


* Added support for sync_single_for_*

* Added support for sync_sg_for_*

* Removed the previous (static) function __dma_sync_page() in favor of 
__dma_sync(), so a single function can be used for all needs. This 
(inline)  function was moved to dma_mapping.h, since it's used by 
dma_cache_sync() there.

* Cache is now flushed on all dma mapping functions, regardless of 
direction. It's obvious for DMA_TO_DEVICE, but not so obvious regarding 
DMA_FROM_DEVICE. The reason in the latter case is that an unflushed 
cache line will be written back to memory sooner or later, possibly 
overwriting DMAed data.

* Cache is never invalidated on dma mapping. It's pointless, since the 
CPU isn't supposed to touch the memory segment anyhow until unmap or sync.

* dma_cache_sync() now really syncs the cache (is was effectively a NOP)


Patch follows.


    Eli



Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
---
 arch/microblaze/include/asm/dma-mapping.h |   20 +++++-
 arch/microblaze/kernel/dma.c              |  109 
++++++++++++++++++++++-------
 2 files changed, 101 insertions(+), 28 deletions(-)

diff --git a/arch/microblaze/include/asm/dma-mapping.h 
b/arch/microblaze/include/asm/dma-mapping.h
index 8fbb0ec..cddeca5 100644
--- a/arch/microblaze/include/asm/dma-mapping.h
+++ b/arch/microblaze/include/asm/dma-mapping.h
@@ -28,12 +28,12 @@
 #include <linux/dma-attrs.h>
 #include <asm/io.h>
 #include <asm-generic/dma-coherent.h>
+#include <asm/cacheflush.h>
 
 #define DMA_ERROR_CODE        (~(dma_addr_t)0x0)
 
 #define __dma_alloc_coherent(dev, gfp, size, handle)    NULL
 #define __dma_free_coherent(size, addr)        ((void)0)
-#define __dma_sync(addr, size, rw)        ((void)0)
 
 static inline unsigned long device_to_mask(struct device *dev)
 {
@@ -95,6 +95,22 @@ static inline int dma_set_mask(struct device *dev, 
u64 dma_mask)
 
 #include <asm-generic/dma-mapping-common.h>
 
+static inline void __dma_sync(unsigned long paddr,
+                  size_t size, enum dma_data_direction direction)
+{
+    switch (direction) {
+    case DMA_TO_DEVICE:
+    case DMA_BIDIRECTIONAL:
+        flush_dcache_range(paddr, paddr + size);
+        break;
+    case DMA_FROM_DEVICE:
+        invalidate_dcache_range(paddr, paddr + size);
+        break;
+    default:
+        BUG();
+    }
+}
+
 static inline int dma_mapping_error(struct device *dev, dma_addr_t 
dma_addr)
 {
     struct dma_map_ops *ops = get_dma_ops(dev);
@@ -135,7 +151,7 @@ static inline void dma_cache_sync(struct device 
*dev, void *vaddr, size_t size,
         enum dma_data_direction direction)
 {
     BUG_ON(direction == DMA_NONE);
-    __dma_sync(vaddr, size, (int)direction);
+    __dma_sync(virt_to_phys(vaddr), size, (int)direction);
 }
 
 #endif    /* _ASM_MICROBLAZE_DMA_MAPPING_H */
diff --git a/arch/microblaze/kernel/dma.c b/arch/microblaze/kernel/dma.c
index 393e6b2..9fa9d82 100644
--- a/arch/microblaze/kernel/dma.c
+++ b/arch/microblaze/kernel/dma.c
@@ -11,7 +11,6 @@
 #include <linux/gfp.h>
 #include <linux/dma-debug.h>
 #include <asm/bug.h>
-#include <asm/cacheflush.h>
 
 /*
  * Generic direct DMA implementation
@@ -21,21 +20,6 @@
  * can set archdata.dma_data to an unsigned long holding the offset. By
  * default the offset is PCI_DRAM_OFFSET.
  */
-static inline void __dma_sync_page(unsigned long paddr, unsigned long 
offset,
-                size_t size, enum dma_data_direction direction)
-{
-    switch (direction) {
-    case DMA_TO_DEVICE:
-    case DMA_BIDIRECTIONAL:
-        flush_dcache_range(paddr + offset, paddr + offset + size);
-        break;
-    case DMA_FROM_DEVICE:
-        invalidate_dcache_range(paddr + offset, paddr + offset + size);
-        break;
-    default:
-        BUG();
-    }
-}
 
 static unsigned long get_dma_direct_offset(struct device *dev)
 {
@@ -91,17 +75,24 @@ static int dma_direct_map_sg(struct device *dev, 
struct scatterlist *sgl,
     /* FIXME this part of code is untested */
     for_each_sg(sgl, sg, nents, i) {
         sg->dma_address = sg_phys(sg) + get_dma_direct_offset(dev);
-        __dma_sync_page(page_to_phys(sg_page(sg)), sg->offset,
-                            sg->length, direction);
+        __dma_sync(page_to_phys(sg_page(sg)) + sg->offset,
+               sg->length, DMA_TO_DEVICE);
     }
 
     return nents;
 }
 
-static void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sg,
+static void dma_direct_unmap_sg(struct device *dev, struct scatterlist 
*sgl,
                 int nents, enum dma_data_direction direction,
                 struct dma_attrs *attrs)
 {
+    struct scatterlist *sg;
+    int i;
+
+    /* FIXME this part of code is untested */
+    if (direction == DMA_FROM_DEVICE)
+        for_each_sg(sgl, sg, nents, i)
+            __dma_sync(sg->dma_address, sg->length, direction);
 }
 
 static int dma_direct_dma_supported(struct device *dev, u64 mask)
@@ -116,7 +107,15 @@ static inline dma_addr_t dma_direct_map_page(struct 
device *dev,
                          enum dma_data_direction direction,
                          struct dma_attrs *attrs)
 {
-    __dma_sync_page(page_to_phys(page), offset, size, direction);
+    /* We're before the DMA transfer, so cache invalidation makes no
+       sense in the case of DMA_FROM_DEVICE. Flushing is necessary
+       in either case, or an unflushed cache line may overwrite
+       data written by device, in the event of that line being allocated
+       for other use. Calling __dma_sync with DMA_TO_DEVICE makes this
+       flush.
+    */
+
+    __dma_sync(page_to_phys(page) + offset, size, DMA_TO_DEVICE);
     return page_to_phys(page) + offset + get_dma_direct_offset(dev);
 }
 
@@ -126,12 +125,66 @@ static inline void dma_direct_unmap_page(struct 
device *dev,
                      enum dma_data_direction direction,
                      struct dma_attrs *attrs)
 {
-/* There is not necessary to do cache cleanup
- *
- * phys_to_virt is here because in __dma_sync_page is __virt_to_phys and
- * dma_address is physical address
- */
-    __dma_sync_page(dma_address, 0 , size, direction);
+/* On a DMA to the device, the data has already been flushed and read by
+   the device at the point unmapping is done. No point doing anything.
+   In the other direction, unmapping may be used just before accessing the
+   data on the CPU, so cache invalidation is necessary.
+*/
+
+    if (direction == DMA_FROM_DEVICE)
+        __dma_sync(dma_address, size, direction);
+}
+
+static inline void
+dma_direct_sync_single_for_cpu(struct device *dev,
+                   dma_addr_t dma_handle, size_t size,
+                   enum dma_data_direction direction)
+{
+    /* It's pointless to invalidate the cache if the device isn't supposed
+       to write to the relevant region */
+
+    if (direction == DMA_FROM_DEVICE)
+        __dma_sync(dma_handle, size, direction);
+}
+
+static inline void
+dma_direct_sync_single_for_device(struct device *dev,
+                  dma_addr_t dma_handle, size_t size,
+                  enum dma_data_direction direction)
+{
+    /* It's pointless to flush the cache if the CPU isn't supposed
+       to write to the relevant region */
+
+    if (direction == DMA_TO_DEVICE)
+        __dma_sync(dma_handle, size, direction);
+}
+
+static inline void
+dma_direct_sync_sg_for_cpu(struct device *dev,
+               struct scatterlist *sgl, int nents,
+               enum dma_data_direction direction)
+{
+    struct scatterlist *sg;
+    int i;
+
+    /* FIXME this part of code is untested */
+    if (direction == DMA_FROM_DEVICE)
+        for_each_sg(sgl, sg, nents, i)
+            __dma_sync(sg->dma_address, sg->length, direction);
+}
+
+static inline void
+dma_direct_sync_sg_for_device(struct device *dev,
+                  struct scatterlist *sgl, int nents,
+                  enum dma_data_direction direction)
+{
+    struct scatterlist *sg;
+    int i;
+
+    /* FIXME this part of code is untested */
+    if (direction == DMA_TO_DEVICE)
+        for_each_sg(sgl, sg, nents, i)
+            __dma_sync(sg->dma_address, sg->length, direction);
 }
 
 struct dma_map_ops dma_direct_ops = {
@@ -142,6 +195,10 @@ struct dma_map_ops dma_direct_ops = {
     .dma_supported    = dma_direct_dma_supported,
     .map_page    = dma_direct_map_page,
     .unmap_page    = dma_direct_unmap_page,
+    .sync_single_for_cpu        = dma_direct_sync_single_for_cpu,
+    .sync_single_for_device        = dma_direct_sync_single_for_device,
+    .sync_sg_for_cpu        = dma_direct_sync_sg_for_cpu,
+    .sync_sg_for_device        = dma_direct_sync_sg_for_device,
 };
 EXPORT_SYMBOL(dma_direct_ops);
 
-- 
1.7.2.2



-- 
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