From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pekka Pietikainen Subject: Re: [PATCH] b44 1GB DMA workaround (was: b44: add 47xx support) Date: Sun, 8 Aug 2004 01:40:19 +0300 Sender: linux-kernel-owner@vger.kernel.org Message-ID: <20040807224019.GA24817@ee.oulu.fi> References: <200407232335.37809.jolt@tuxbox.org> <20040726141128.GA5435@ee.oulu.fi> <20040804003108.GA10445@ee.oulu.fi> <20040803183919.2990d045.davem@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Cc: jgarzik@pobox.com, jolt@tuxbox.org, linux-kernel@vger.kernel.org, netdev@oss.sgi.com Return-path: To: "David S. Miller" Content-Disposition: inline In-Reply-To: <20040803183919.2990d045.davem@redhat.com> List-Id: netdev.vger.kernel.org On Tue, Aug 03, 2004 at 06:39:19PM -0700, David S. Miller wrote: > Changing skb->data is not legal. Please implement this in > such a way that skb->data does not get modified. By modifying > skb->data you will break things such as packet sniffers and > netfilter, and that's just the tip of the iceberg. :-) > Haven't noticed any breakage (tm) but I'm just a x86 weenie :-) Current approach is: if(1 (just for testing ;) ) || mapping+len > B44_DMA_MASK) { /* Chip can't handle DMA to/from >1GB, use bounce buffer */ pci_unmap_single(bp->pdev, mapping, len,PCI_DMA_TODEVICE); memcpy(bp->tx_bufs+entry*TX_PKT_BUF_SZ,skb->data,skb->len); mapping = pci_map_single(bp->pdev,bp->tx_bufs+entry*TX_PKT_BUF_SZ, len, PCI_DMA_TODEVICE); } Which also works (tm). Setting the skb to a special value seems a bit tricky as skb->len is used in b44_tx for that nop^H^H^Hpci_unmap_single. It looks to me as the right things when the code gets changed as above (even for archs where the unmapping is not a nop) get done, but I could easily be missing something. -- Pekka Pietikainen