common: add dma_mmap_from_coherent() function

Add a common helper for dma-mapping core for mapping a coherent buffer
to userspace.

Reported-by: Subash Patel <subashrp@gmail.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Tested-By: Subash Patel <subash.ramaswamy@linaro.org>

2 files changed, 45 insertions, 1 deletions

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index bb0025c510b3..1b85949e3d2f 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -10,6 +10,7 @@
 struct dma_coherent_mem {
         void            *virt_base;
         dma_addr_t      device_base;
+        phys_addr_t     pfn_base;
         int             size;
         int             flags;
         unsigned long   *bitmap;
@@ -44,6 +45,7 @@ int dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
 
         dev->dma_mem->virt_base = mem_base;
         dev->dma_mem->device_base = device_addr;
+        dev->dma_mem->pfn_base = PFN_DOWN(bus_addr);
         dev->dma_mem->size = pages;
         dev->dma_mem->flags = flags;
 
@@ -176,3 +178,43 @@ int dma_release_from_coherent(struct device *dev, int order, void *vaddr)
         return 0;
 }
 EXPORT_SYMBOL(dma_release_from_coherent);
+
+/**
+ * dma_mmap_from_coherent() - try to mmap the memory allocated from
+ * per-device coherent memory pool to userspace
+ * @dev:        device from which the memory was allocated
+ * @vma:        vm_area for the userspace memory
+ * @vaddr:      cpu address returned by dma_alloc_from_coherent
+ * @size:       size of the memory buffer allocated by dma_alloc_from_coherent
+ *
+ * This checks whether the memory was allocated from the per-device
+ * coherent memory pool and if so, maps that memory to the provided vma.
+ *
+ * Returns 1 if we correctly mapped the memory, or 0 if
+ * dma_release_coherent() should proceed with mapping memory from
+ * generic pools.
+ */
+int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma,
+                           void *vaddr, size_t size, int *ret)
+{
+        struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
+
+        if (mem && vaddr >= mem->virt_base && vaddr + size <=
+                   (mem->virt_base + (mem->size << PAGE_SHIFT))) {
+                unsigned long off = vma->vm_pgoff;
+                int start = (vaddr - mem->virt_base) >> PAGE_SHIFT;
+                int user_count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+                int count = size >> PAGE_SHIFT;
+
+                *ret = -ENXIO;
+                if (off < count && user_count <= count - off) {
+                        unsigned pfn = mem->pfn_base + start + off;
+                        *ret = remap_pfn_range(vma, vma->vm_start, pfn,
+                                               user_count << PAGE_SHIFT,
+                                               vma->vm_page_prot);
+                }
+                return 1;
+        }
+        return 0;
+}
+EXPORT_SYMBOL(dma_mmap_from_coherent);
diff --git a/include/asm-generic/dma-coherent.h b/include/asm-generic/dma-coherent.h
index 85a3ffaa0242..abfb2682de7f 100644
--- a/include/asm-generic/dma-coherent.h
+++ b/include/asm-generic/dma-coherent.h
@@ -3,13 +3,15 @@
 
 #ifdef CONFIG_HAVE_GENERIC_DMA_COHERENT
 /*
- * These two functions are only for dma allocator.
+ * These three functions are only for dma allocator.
  * Don't use them in device drivers.
  */
 int dma_alloc_from_coherent(struct device *dev, ssize_t size,
                                        dma_addr_t *dma_handle, void **ret);
 int dma_release_from_coherent(struct device *dev, int order, void *vaddr);
 
+int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma,
+                            void *cpu_addr, size_t size, int *ret);
 /*
  * Standard interface
  */