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SubjectRe: [discuss] Re: 32-bit dma allocations on 64-bit platforms
At Thu, 24 Jun 2004 13:29:00 +0200,
Andi Kleen wrote:
>
> > Can't it be called with GFP_KERNEL at first, then with GFP_DMA if the
> > allocated pages are out of dma mask, just like in pci-gart.c?
> > (with ifdef x86-64)
>
> That won't work reliable enough in extreme cases.

Well, it's not perfect, but it'd be far better than GFP_DMA only :)


BTW, we have the similar problem on i386, too. The non-32bit DMA mask
always results in the allocation with GFP_DMA. The patch below does
similar hack as described above, calling with GFP_DMA as fallback.


Takashi

--- linux-2.6.7/arch/i386/kernel/pci-dma.c 2004-06-24 15:56:46.017473544 +0200
+++ linux-2.6.7/arch/i386/kernel/pci-dma.c 2004-06-24 16:05:02.449803937 +0200
@@ -17,17 +17,35 @@ void *dma_alloc_coherent(struct device *
dma_addr_t *dma_handle, int gfp)
{
void *ret;
+ unsigned long dma_mask;
+
/* ignore region specifiers */
gfp &= ~(__GFP_DMA | __GFP_HIGHMEM);

- if (dev == NULL || (dev->coherent_dma_mask < 0xffffffff))
+ if (dev == NULL) {
gfp |= GFP_DMA;
+ dma_mask = 0xffffffUL;
+ } else {
+ dma_mask = 0xffffffffUL;
+ if (dev->dma_mask)
+ dma_mask = *dev->dma_mask;
+ if (dev->coherent_dma_mask)
+ dma_mask &= (unsigned long)dev->coherent_dma_mask;
+ }

+ again:
ret = (void *)__get_free_pages(gfp, get_order(size));

if (ret != NULL) {
- memset(ret, 0, size);
*dma_handle = virt_to_phys(ret);
+ if (((unsigned long)*dma_handle + size - 1) & ~dma_mask) {
+ free_pages((unsigned long)ret, get_order(size));
+ if (gfp & GFP_DMA)
+ return NULL;
+ gfp |= GFP_DMA;
+ goto again;
+ }
+ memset(ret, 0, size);
}
return ret;
}
-
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