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Subject[RFC PATCH] dma: Add barrierless dma mapping/unmapping api
Date
From: Abhijeet Dharmapurikar <adharmap@quicinc.com>

Tests have shown that there is a significant performance gain
when a driver uses mapping/unmapping functions without a barrier
multiple times and calls dsb() only after the last buffer. This
api adds support for barrierless dma operations on ARMv6
and ARMv7.

Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
---
Please refer to the earlier post here http://lkml.org/lkml/2010/1/4/347.
These changes only are only for the arm v6 and v7
architecture and introduce dma_map/unmap_single_nobarrier api.
The idea is to extend the cpu_cache_fns.dma_.*_range functions to accept
a third boolean argument that tells it whether to execute the barrier or
skip it. Note that this applies over Linux 2.6.33-rc5 and needs a few changes
to apply on the linux-next tree.


arch/arm/include/asm/cacheflush.h | 12 ++++----
arch/arm/include/asm/dma-mapping.h | 57 ++++++++++++++++++++++++++++++++++--
arch/arm/mm/cache-v6.S | 15 ++++++----
arch/arm/mm/cache-v7.S | 19 +++++++++++-
arch/arm/mm/dma-mapping.c | 17 ++++++-----
drivers/staging/dream/pmem.c | 4 +-
6 files changed, 97 insertions(+), 27 deletions(-)
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index c77d2fa..59ce7fb 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -227,9 +227,9 @@ struct cpu_cache_fns {
void (*coherent_user_range)(unsigned long, unsigned long);
void (*flush_kern_dcache_area)(void *, size_t);

- void (*dma_inv_range)(const void *, const void *);
- void (*dma_clean_range)(const void *, const void *);
- void (*dma_flush_range)(const void *, const void *);
+ void (*dma_inv_range)(const void *, const void *, unsigned long);
+ void (*dma_clean_range)(const void *, const void *, unsigned long);
+ void (*dma_flush_range)(const void *, const void *, unsigned long);
};

struct outer_cache_fns {
@@ -288,9 +288,9 @@ extern void __cpuc_flush_dcache_area(void *, size_t);
#define dmac_clean_range __glue(_CACHE,_dma_clean_range)
#define dmac_flush_range __glue(_CACHE,_dma_flush_range)

-extern void dmac_inv_range(const void *, const void *);
-extern void dmac_clean_range(const void *, const void *);
-extern void dmac_flush_range(const void *, const void *);
+extern void dmac_inv_range(const void *, const void *, unsigned long);
+extern void dmac_clean_range(const void *, const void *, unsigned long);
+extern void dmac_flush_range(const void *, const void *, unsigned long);

#endif

diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
index a96300b..066923c 100644
--- a/arch/arm/include/asm/dma-mapping.h
+++ b/arch/arm/include/asm/dma-mapping.h
@@ -66,7 +66,8 @@ static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
* platforms with CONFIG_DMABOUNCE.
* Use the driver DMA support - see dma-mapping.h (dma_sync_*)
*/
-extern void dma_cache_maint(const void *kaddr, size_t size, int rw);
+extern void dma_cache_maint(const void *kaddr, size_t size, int rw,
+ unsigned long barrier);
extern void dma_cache_maint_page(struct page *page, unsigned long offset,
size_t size, int rw);

@@ -297,6 +298,7 @@ static inline int dmabounce_sync_for_device(struct device *d, dma_addr_t addr,
*
* The device owns this memory once this call has completed. The CPU
* can regain ownership by calling dma_unmap_single() or
+ * or dma_unmap_single_nobarrier followed by dsb/dmb or
* dma_sync_single_for_cpu().
*/
static inline dma_addr_t dma_map_single(struct device *dev, void *cpu_addr,
@@ -305,12 +307,40 @@ static inline dma_addr_t dma_map_single(struct device *dev, void *cpu_addr,
BUG_ON(!valid_dma_direction(dir));

if (!arch_is_coherent())
- dma_cache_maint(cpu_addr, size, dir);
+ dma_cache_maint(cpu_addr, size, dir, 1);

return virt_to_dma(dev, cpu_addr);
}

/**
+ * dma_map_single_nobarrier - map a single buffer for streaming DMA
+ * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
+ * @cpu_addr: CPU direct mapped address of buffer
+ * @size: size of buffer to map
+ * @dir: DMA transfer direction
+ *
+ * Ensure that any data held in the cache is appropriately discarded
+ * or written back.
+ *
+ * The device owns this memory once this call has completed and a dsb is
+ * executed. The CPU
+ * can regain ownership by calling dma_unmap_single() or
+ * dma_map_single_nobarrier followed by dsb() or
+ * dma_sync_single_for_cpu().
+ */
+static inline dma_addr_t dma_map_single_nobarrier(struct device *dev,
+ void *cpu_addr, size_t size, enum dma_data_direction dir)
+{
+ BUG_ON(!valid_dma_direction(dir));
+
+ if (!arch_is_coherent())
+ dma_cache_maint(cpu_addr, size, dir, 0);
+
+ return virt_to_dma(dev, cpu_addr);
+}
+
+
+/**
* dma_map_page - map a portion of a page for streaming DMA
* @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
* @page: page that buffer resides in
@@ -356,6 +386,26 @@ static inline void dma_unmap_single(struct device *dev, dma_addr_t handle,
}

/**
+ * dma_unmap_single_nobarrier - unmap a single buffer previously mapped
+ * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
+ * @handle: DMA address of buffer
+ * @size: size of buffer (same as passed to dma_map_single)
+ * @dir: DMA transfer direction (same as passed to dma_map_single)
+ *
+ * Unmap a single streaming mode DMA translation. The handle and size
+ * must match what was provided in the previous dma_map_single() call.
+ * All other usages are undefined.
+ *
+ * After this call, and a dsb(), reads by the CPU to the buffer are
+ * guaranteed to see whatever the device wrote there.
+ */
+static inline void dma_unmap_single_nobarrier(struct device *dev,
+ dma_addr_t handle, size_t size, enum dma_data_direction dir)
+{
+ /* nothing to do */
+}
+
+/**
* dma_unmap_page - unmap a buffer previously mapped through dma_map_page()
* @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
* @handle: DMA address of buffer
@@ -413,7 +463,8 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
return;

if (!arch_is_coherent())
- dma_cache_maint(dma_to_virt(dev, handle) + offset, size, dir);
+ dma_cache_maint(dma_to_virt(dev, handle) + offset,
+ size, dir, 1);
}

static inline void dma_sync_single_for_cpu(struct device *dev,
diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S
index 4ba0a24..a88ab56 100644
--- a/arch/arm/mm/cache-v6.S
+++ b/arch/arm/mm/cache-v6.S
@@ -186,7 +186,7 @@ ENTRY(v6_flush_kern_dcache_area)


/*
- * v6_dma_inv_range(start,end)
+ * v6_dma_inv_range(start,end,barrier)
*
* Invalidate the data cache within the specified region; we will
* be performing a DMA operation in this region and we want to
@@ -220,11 +220,12 @@ ENTRY(v6_dma_inv_range)
cmp r0, r1
blo 1b
mov r0, #0
- mcr p15, 0, r0, c7, c10, 4 @ drain write buffer
+ cmp r2, #1
+ mcreq p15, 0, r0, c7, c10, 4 @ drain write buffer
mov pc, lr

/*
- * v6_dma_clean_range(start,end)
+ * v6_dma_clean_range(start,end,barrier)
* - start - virtual start address of region
* - end - virtual end address of region
*/
@@ -240,11 +241,12 @@ ENTRY(v6_dma_clean_range)
cmp r0, r1
blo 1b
mov r0, #0
- mcr p15, 0, r0, c7, c10, 4 @ drain write buffer
+ cmp r2, #1
+ mcreq p15, 0, r0, c7, c10, 4 @ drain write buffer
mov pc, lr

/*
- * v6_dma_flush_range(start,end)
+ * v6_dma_flush_range(start,end,barrier)
* - start - virtual start address of region
* - end - virtual end address of region
*/
@@ -260,7 +262,8 @@ ENTRY(v6_dma_flush_range)
cmp r0, r1
blo 1b
mov r0, #0
- mcr p15, 0, r0, c7, c10, 4 @ drain write buffer
+ cmp r2, #1
+ mcreq p15, 0, r0, c7, c10, 4 @ drain write buffer
mov pc, lr

__INITDATA
diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S
index 9073db8..147a325 100644
--- a/arch/arm/mm/cache-v7.S
+++ b/arch/arm/mm/cache-v7.S
@@ -217,6 +217,7 @@ ENDPROC(v7_flush_kern_dcache_area)
* - end - virtual end address of region
*/
ENTRY(v7_dma_inv_range)
+ str r2,[sp, #-4]!
dcache_line_size r2, r3
sub r3, r2, #1
tst r0, r3
@@ -231,16 +232,21 @@ ENTRY(v7_dma_inv_range)
add r0, r0, r2
cmp r0, r1
blo 1b
+ ldr r2, [sp], #4
+ cmp r2, #1
+ bne 2f
dsb
+2:
mov pc, lr
ENDPROC(v7_dma_inv_range)

/*
- * v7_dma_clean_range(start,end)
+ * v7_dma_clean_range(start,end,barrier)
* - start - virtual start address of region
* - end - virtual end address of region
*/
ENTRY(v7_dma_clean_range)
+ str r2,[sp, #-4]!
dcache_line_size r2, r3
sub r3, r2, #1
bic r0, r0, r3
@@ -249,16 +255,21 @@ ENTRY(v7_dma_clean_range)
add r0, r0, r2
cmp r0, r1
blo 1b
+ ldr r2, [sp], #4
+ cmp r2, #1
+ bne 2f
dsb
+2:
mov pc, lr
ENDPROC(v7_dma_clean_range)

/*
- * v7_dma_flush_range(start,end)
+ * v7_dma_flush_range(start,end,barrier)
* - start - virtual start address of region
* - end - virtual end address of region
*/
ENTRY(v7_dma_flush_range)
+ str r2,[sp, #-4]!
dcache_line_size r2, r3
sub r3, r2, #1
bic r0, r0, r3
@@ -267,7 +278,11 @@ ENTRY(v7_dma_flush_range)
add r0, r0, r2
cmp r0, r1
blo 1b
+ ldr r2, [sp], #4
+ cmp r2, #1
+ bne 2f
dsb
+2:
mov pc, lr
ENDPROC(v7_dma_flush_range)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 26325cb..c9e3124 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -106,7 +106,7 @@ static struct page *__dma_alloc_buffer(struct device *dev, size_t size, gfp_t gf
*/
ptr = page_address(page);
memset(ptr, 0, size);
- dmac_flush_range(ptr, ptr + size);
+ dmac_flush_range(ptr, ptr + size, 1);
outer_flush_range(__pa(ptr), __pa(ptr) + size);

return page;
@@ -404,10 +404,11 @@ EXPORT_SYMBOL(dma_free_coherent);
* platforms with CONFIG_DMABOUNCE.
* Use the driver DMA support - see dma-mapping.h (dma_sync_*)
*/
-void dma_cache_maint(const void *start, size_t size, int direction)
+void dma_cache_maint(const void *start, size_t size, int direction,
+ unsigned long barrier)
{
- void (*inner_op)(const void *, const void *);
- void (*outer_op)(unsigned long, unsigned long);
+ void (*inner_op)(const void *, const void *, unsigned long);
+ void (*outer_op)(unsigned long, unsigned long, unsigned long);

BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(start + size - 1));

@@ -428,7 +429,7 @@ void dma_cache_maint(const void *start, size_t size, int direction)
BUG();
}

- inner_op(start, start + size);
+ inner_op(start, start + size, barrier);
outer_op(__pa(start), __pa(start) + size);
}
EXPORT_SYMBOL(dma_cache_maint);
@@ -438,7 +439,7 @@ static void dma_cache_maint_contiguous(struct page *page, unsigned long offset,
{
void *vaddr;
unsigned long paddr;
- void (*inner_op)(const void *, const void *);
+ void (*inner_op)(const void *, const void *, unsigned long);
void (*outer_op)(unsigned long, unsigned long);

switch (direction) {
@@ -460,12 +461,12 @@ static void dma_cache_maint_contiguous(struct page *page, unsigned long offset,

if (!PageHighMem(page)) {
vaddr = page_address(page) + offset;
- inner_op(vaddr, vaddr + size);
+ inner_op(vaddr, vaddr + size, 1);
} else {
vaddr = kmap_high_get(page);
if (vaddr) {
vaddr += offset;
- inner_op(vaddr, vaddr + size);
+ inner_op(vaddr, vaddr + size, 1);
kunmap_high(page);
}
}
diff --git a/drivers/staging/dream/pmem.c b/drivers/staging/dream/pmem.c
index def6468..1b24945 100644
--- a/drivers/staging/dream/pmem.c
+++ b/drivers/staging/dream/pmem.c
@@ -802,7 +802,7 @@ void flush_pmem_file(struct file *file, unsigned long offset, unsigned long len)
vaddr = pmem_start_vaddr(id, data);
/* if this isn't a submmapped file, flush the whole thing */
if (unlikely(!(data->flags & PMEM_FLAGS_CONNECTED))) {
- dmac_flush_range(vaddr, vaddr + pmem_len(id, data));
+ dmac_flush_range(vaddr, vaddr + pmem_len(id, data), 1);
goto end;
}
/* otherwise, flush the region of the file we are drawing */
@@ -813,7 +813,7 @@ void flush_pmem_file(struct file *file, unsigned long offset, unsigned long len)
region_node->region.len))) {
flush_start = vaddr + region_node->region.offset;
flush_end = flush_start + region_node->region.len;
- dmac_flush_range(flush_start, flush_end);
+ dmac_flush_range(flush_start, flush_end, 1);
break;
}
}
--
1.5.6.3


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