Postpone calling virt_to_page() translation on memory locations not
guaranteed to be backed by a struct page. Try first to map memory from
device's coherent memory pool, then perform translation if that fails.

On some architectures, specifically SH when configured with SPARSEMEM
memory model, assuming a struct page is always assigned to a memory
address lead to unexpected hangs during the virtual to page address
translation. This patch fixes that specific issue but applies in the
general case too.

Suggested-by: Laurent Pinchart <>
Signed-off-by: Jacopo Mondi <>


It has now been clarified this patch does not resolve the issue, but only
mitigate it on platforms where dma_mmap_from_dev_coherent() succeeds and
delay page_to_pfn() faulty conversion.

A suggested proper solution would be not relying on dma_common_mmap() but
require all platforms to implement an mmap methods known to work, as noted
by Christoph in v1 review.

v1 -> v2:
- Save the 'pfn' temp variable performing the page_to_pfn() conversion in the
  remap_pfn_range() function call as suggested by Christoph.

 drivers/base/dma-mapping.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
index 3b11835..d82566d 100644
--- a/drivers/base/dma-mapping.c
+++ b/drivers/base/dma-mapping.c
@@ -226,7 +226,6 @@ int dma_common_mmap(struct device *dev, struct 
vm_area_struct *vma,
        unsigned long user_count = vma_pages(vma);
        unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-       unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
        unsigned long off = vma->vm_pgoff;

        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
@@ -234,12 +233,11 @@ int dma_common_mmap(struct device *dev, struct 
vm_area_struct *vma,
        if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
                return ret;

-       if (off < count && user_count <= (count - off)) {
+       if (off < count && user_count <= (count - off))
                ret = remap_pfn_range(vma, vma->vm_start,
-                                     pfn + off,
+                                     page_to_pfn(virt_to_page(cpu_addr)) + off,
                                      user_count << PAGE_SHIFT,
-       }

        return ret;

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