On Mon, Nov 21, 2005 at 05:17:12PM +0100, Takashi Iwai wrote:
> Now another question arises: Which is the recommended method for
> mmapping RAM pages, vma nopage callback or remap_pfn_range()?
>
> IIRC, in the ealier versions, the former was recommended because
> remap_page_range() with page-reserve was regarded as a hack.
> But, looking through these changes, I feel that remap_pfn_range() is
> better (easier and stabler) than vma nopage...
And this brings up the question of this age old patch:
diff -up -x BitKeeper -x ChangeSet -x SCCS -x _xlk -x '*.orig' -x '*.rej' -r orig/arch/i386/kernel/pci-dma.c linux/arch/i386/kernel/pci-dma.c
--- orig/arch/i386/kernel/pci-dma.c Mon Apr 4 22:52:57 2005
+++ linux/arch/i386/kernel/pci-dma.c Mon Apr 4 22:44:45 2005
@@ -50,7 +50,7 @@ void *dma_alloc_coherent(struct device *
ret = (void *)__get_free_pages(gfp, order);
if (ret != NULL) {
- memset(ret, 0, size);
+ memset(ret, 0, PAGE_ALIGN(size));
*dma_handle = virt_to_phys(ret);
}
return ret;
diff -up -x BitKeeper -x ChangeSet -x SCCS -x _xlk -x '*.orig' -x '*.rej' -r orig/include/asm-i386/dma-mapping.h linux/include/asm-i386/dma-mapping.h
--- orig/include/asm-i386/dma-mapping.h Mon Apr 4 22:54:41 2005
+++ linux/include/asm-i386/dma-mapping.h Mon Apr 4 22:48:11 2005
@@ -16,6 +16,23 @@ void *dma_alloc_coherent(struct device *
void dma_free_coherent(struct device *dev, size_t size,
void *vaddr, dma_addr_t dma_handle);
+static inline int
+dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma,
+ void *vaddr, dma_addr_t handle, size_t size)
+{
+ unsigned long offset = vma->vm_pgoff, usize;
+
+ size = PAGE_ALIGN(size) >> PAGE_SHIFT;
+ usize = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+
+ if (offset >= size || usize > (size - offset))
+ return -ENXIO;
+
+ return remap_page_range(vma, vma->vm_start,
+ __pa(vaddr) + (offset << PAGE_SHIFT),
+ usize << PAGE_SHIFT, vma->vm_page_prot);
+}
+
static inline dma_addr_t
dma_map_single(struct device *dev, void *ptr, size_t size,
enum dma_data_direction direction)
which provides the dma mmap API which presently is ARM-only on to x86.
Note: the first part of this patch should probably be applied anyway
if you're mmaping dma_alloc_coherent pages to userspace to ensure that
information is not leaked from kernel context.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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