Re: [PATCH 8/9] swiotlb: support HIGHMEM in swiotlb_bus_to_virt

From: Jeremy Fitzhardinge
Date: Fri May 29 2009 - 11:58:24 EST

Ian Campbell wrote:
Rather than supplying a __weak hook which architectures which support
highmem can overide simply provide a version of swiotlb_bus_to_virt
which works with high memory. Make it conditional since it is a more
expensive variant than the non-highmem version.

Acutal function contents taken from the PowerPC swiotlb patchset by
Becky Bruce.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Becky Bruce <beckyb@xxxxxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Kumar Gala <galak@xxxxxxxxxxxxxxxxxxx>
Cc: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxx
lib/swiotlb.c | 14 +++++++++++++-
1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index e332342..c50a5ed 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -130,10 +130,22 @@ static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
return phys_to_dma(hwdev, virt_to_phys(address));
-void * __weak swiotlb_bus_to_virt(struct device *hwdev, dma_addr_t address)
+static void * swiotlb_bus_to_virt(struct device *hwdev, dma_addr_t address)

I think it would be better to put the #ifdef within the function body so that there's no chance of prototype-drift.
+ unsigned long pfn = PFN_DOWN(dma_to_phys(hwdev, addr));
+ void *pageaddr = page_address(pfn_to_page(pfn));
+ if (pageaddr != NULL)
+ return pageaddr + (addr % PAGE_SIZE);
Is there an arch-independent test to see if a pfn is considered highmem or not (which returns a constant on non-highmem configurations)? If so, then I think this could be common without having to go via a struct page.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at