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


--
Web: http://www.billauer.co.il



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