From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 4 Apr 2002 09:35:58 +1000 From: David Gibson To: linuxppc-embedded@lists.linuxppc.org Subject: Re: Workaround for USB DMA bugs Message-ID: <20020403233558.GF21034@zax> References: <20020403024321.GN1026@zax> <3CAACF45.8090003@elsoft.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <3CAACF45.8090003@elsoft.ch> Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: On Wed, Apr 03, 2002 at 11:45:41AM +0200, "David M?ller (ELSOFT AG)" wrote: > Hello > > David Gibson wrote: > >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 > >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); > > Cool. This hack fixes a problem i see with the USB stack on our boards > since quite some time. > > What about replacing "#ifdef CONFIG_USB" by > "#if defined(CONFIG_USB) || defined(CONFIG_USB_MODULE)" so this > workaround works also if the USB stack is compiled with module support > enabled. It might be safer / cleaner just to unconditionally enable it, as Dan Malek suggested. > BTW > Do you know from which version of the 2.5 kernel on this buffer > alignment problem is fixed? No, I just happened to see a message from one of the USB people (Greg K-H IIRC) saying he thought it was fixed in 2.5 and that they'd like people to report any remaining non-cache-aligned buffers. -- David Gibson | For every complex problem there is a david@gibson.dropbear.id.au | solution which is simple, neat and | wrong. -- H.L. Mencken http://www.ozlabs.org/people/dgibson ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/