Subject: Workaround for USB DMA bugs

From: David Gibson <[email-masked]>
Date: Wed, 3 Apr 2002 12:43:22 +1000

Well, I'm not sure I'd want to pollute the tree with this sort of
hack, but on the other hand it makes things work that wouldn't
otherwise.

Does anyone think it's a good idea to commit the following patch:

diff -urN /home/dgibson/kernel/linuxppc_2_4_devel/arch/ppc/mm/cachemap.c linux-grinch/arch/ppc/mm/cachemap.c
--- /home/dgibson/kernel/linuxppc_2_4_devel/arch/ppc/mm/cachemap.c	Thu Mar 14 13:49:01 2002
+++ linux-grinch/arch/ppc/mm/cachemap.c	Wed Apr  3 11:51:30 2002
@@ -137,7 +137,18 @@
 	case PCI_DMA_NONE:
 		BUG();
 	case PCI_DMA_FROMDEVICE:	/* invalidate only */
+#ifdef CONFIG_USB
+		/* The USB stack is broken in that it uses DMA buffers
+                   on the stack which are on the stack and not
+                   cacheline aligned.  That means cache invalidates
+                   before DMA transfers corrupt the stack on machines
+                   without DMA-consistent cache.  This is a nasty
+                   workaround until the USB layer is fixed (apparently
+                   done in 2.5). */
+		flush_dcache_range(start, end);
+#else
 		invalidate_dcache_range(start, end);
+#endif
 		break;
 	case PCI_DMA_TODEVICE:		/* writeback only */
 		clean_dcache_range(start, end);

--
David Gibson			| For every complex problem there is a
[email-masked]	| solution which is simple, neat and
				| wrong.  -- H.L. Mencken
http://www.ozlabs.org/people/dgibson

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