Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753806Ab0HMVyd (ORCPT ); Fri, 13 Aug 2010 17:54:33 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:55542 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752880Ab0HMVyc (ORCPT ); Fri, 13 Aug 2010 17:54:32 -0400 Date: Fri, 13 Aug 2010 22:54:13 +0100 From: Russell King - ARM Linux To: FUJITA Tomonori Cc: khc@pm.waw.pl, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?) Message-ID: <20100813215413.GA21607@n2100.arm.linux.org.uk> References: <20100811110448S.fujita.tomonori@lab.ntt.co.jp> <20100811072532.GA21511@n2100.arm.linux.org.uk> <20100813152224H.fujita.tomonori@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100813152224H.fujita.tomonori@lab.ntt.co.jp> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1366 Lines: 30 On Fri, Aug 13, 2010 at 03:23:53PM +0900, FUJITA Tomonori wrote: > On Wed, 11 Aug 2010 08:25:32 +0100 > Russell King - ARM Linux wrote: > > It doesn't break dmabounce. > > > > What it breaks is the fact that a PCI device which can do 32-bit DMA is > > connected to a PCI bus which can only access the first 64MB of memory > > through the host bridge, but the system has more than 64MB available. > > > > Allowing a 32-bit DMA mask means that dmabounce can't detect that memory > > above 64MB needs to be bounced to memory below the 64MB boundary. > > But dmabounce doesn't look at dev->coherent_dma_mask. > > The change breaks __dma_alloc_buffer()? If we set dev->coherent_dma_mask > to DMA_BIT_MASK(32) for ixp4xx's pci devices, __dma_alloc_buffer() > doesn't use GFP_DMA. With an incorrect coherent_dma_mask, dma_alloc_coherent() will return memory outside of the 64MB window. This means that when dmabounce comes to allocate the replacement buffer, it gets a buffer which won't be accessible to the DMA controller - which is a condition it doesn't check for. Ergo, it breaks dmabounce. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/