Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=cdcc520d7b73445c3552a70786afed9a2b22c010
Commit: cdcc520d7b73445c3552a70786afed9a2b22c010
Parent: 01faccbf866195831af202de59f37e29467a3d74
Author: Chris Snook <[EMAIL PROTECTED]>
AuthorDate: Thu Sep 20 15:57:15 2007 -0400
Committer: David S. Miller <[EMAIL PROTECTED]>
CommitDate: Wed Oct 10 16:53:49 2007 -0700
atl1: explain 32-bit DMA restriction
Document the fact that atl1 uses a single shared register for the high 32
bits of 64-bit DMA addresses, making 64-bit DMA more trouble than it's
worth.
Signed-off-by: Chris Snook <[EMAIL PROTECTED]>
Signed-off-by: Jeff Garzik <[EMAIL PROTECTED]>
---
drivers/net/atl1/atl1_main.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/net/atl1/atl1_main.c b/drivers/net/atl1/atl1_main.c
index e1a9223..4c728f1 100644
--- a/drivers/net/atl1/atl1_main.c
+++ b/drivers/net/atl1/atl1_main.c
@@ -2209,8 +2209,14 @@ static int __devinit atl1_probe(struct pci_dev *pdev,
return err;
/*
- * 64-bit DMA currently has data corruption problems, so let's just
- * use 32-bit DMA for now. This is a big hack that is probably wrong.
+ * The atl1 chip can DMA to 64-bit addresses, but it uses a single
+ * shared register for the high 32 bits, so only a single, aligned,
+ * 4 GB physical address range can be used at a time.
+ *
+ * Supporting 64-bit DMA on this hardware is more trouble than it's
+ * worth. It is far easier to limit to 32-bit DMA than update
+ * various kernel subsystems to support the mechanics required by a
+ * fixed-high-32-bit system.
*/
err = pci_set_dma_mask(pdev, DMA_32BIT_MASK);
if (err) {
-
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