Re: [PATCH 03/10] x86: add initialization code for DMA-API debugging

On Sat, 22 Nov 2008 19:16:05 +0900
FUJITA Tomonori [off-list ref] wrote:

On Sat, 22 Nov 2008 10:40:32 +0100
Joerg Roedel [off-list ref] wrote:

quoted

quoted

quoted

+static int hash_fn(struct dma_debug_entry *entry)
+{
+	/*
+	 * Hash function is based on the dma address.
+	 * We use bits 20-27 here as the index into the hash
+	 */
+	BUG_ON(entry->dev_addr == bad_dma_address);

'bad_dma_address' is x86 specific. You already found it though.

Interesting. Is there another value for dma_addr_t which drivers can
check for to find out if a dma-api operation failed?

They are architecture dependent. But only X86 uses a variable because
of GART and swiotlb, I think.

BTW, this code doesn't work even on x86 (swiotlb). dma_map_error
should be used, which is an architecture-independent way to test a dma
address.