From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754356AbaKSMtQ (ORCPT ); Wed, 19 Nov 2014 07:49:16 -0500 Received: from mout.kundenserver.de ([212.227.126.130]:63421 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753832AbaKSMtP (ORCPT ); Wed, 19 Nov 2014 07:49:15 -0500 From: Arnd Bergmann To: Catalin Marinas Cc: Ding Tianhong , "linux-arm-kernel@lists.infradead.org" , Will Deacon , "linux-kernel@vger.kernel.org" Subject: Re: For the problem when using swiotlb Date: Wed, 19 Nov 2014 13:48:58 +0100 Message-ID: <1497289.TPKf3qDiKk@wuerfel> User-Agent: KMail/4.11.5 (Linux/3.16.0-10-generic; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20141119112910.GD7156@e104818-lin.cambridge.arm.com> References: <5469E26B.2010905@huawei.com> <1535751.CcvIi3DN4F@wuerfel> <20141119112910.GD7156@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V02:K0:I/ptBz8IY1PTelI/3CedNpeATcr7n1roYOoY2NSahs+ hFpnKBTtKH6sExYGQNaPlU77nwL4gUn9SFADgLCS75ZotXeZlf iQTY+M6IpGN+bX8tXv1M8BAGxUyVstezWEPxm9lL+XdwYQNZFQ JuzMT+2X8wOSSClRsa1E2koJzCmADQC9oPzOtnpHi1+Qj1N4Tn SyWBfcJOccalAgYwxEtIhBolwzwDUp5tEZ5WVmn8Am4gnoqNAb k5Z6Zge5YLGGQra+zhJtDOBEKTkdhsTjEZTmgIvXrNTH7L5Giq 6jSqUiLPJDbeU96wrZs+PAqFACJhstn9IRzqLuC28/oMwA8I0E H4g/yh5O6sh7GcYy+M+Y= X-UI-Out-Filterresults: notjunk:1; Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 19 November 2014 11:29:10 Catalin Marinas wrote: > > The driver should call 'dma_set_mask_and_coherent()' with the appropriate > > dma mask, and check whether that succeeded. However, the code implementing > > dma_set_mask_and_coherent on arm64 also needs to be changed to look up > > the dma-ranges property (see of_dma_configure()), and check if the mask > > is possible. > > dma_set_mask_and_coherent() is a generic function. I think the > of_dma_configure() should start with a coherent_dma_mask based on > dma-ranges if given rather than defaulting to DMA_BIT_MASK(32). The > comment in of_dma_configure() says that devices should set up the > supported mask but it's not always up to them but the bus they are > connected to. > > Something like below, untested: > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > index 3b64d0bf5bba..dff34883db45 100644 > --- a/drivers/of/platform.c > +++ b/drivers/of/platform.c > @@ -200,6 +200,10 @@ static void of_dma_configure(struct device *dev) > /* DMA ranges found. Calculate and set dma_pfn_offset */ > dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr); > dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset); > + > + /* Set the coherent_dma_mask based on the dma-ranges property */ > + if (size) > + dev->coherent_dma_mask = DMA_BIT_MASK(ilog2(size)); > } > > We have discussed this in the past, and the problem with this is that the actual mask depends both on the capabilities of the device and the bus. In particular, if the device can only do 32-bit DMA, we must not set the mask to something higher. The normal rule here is that a driver that wants to do 64-bit DMA must call dma_set_mask_and_coherent() with the higher mask, while a device that can not access all of the 32-bit address space must call dma_set_mask_and_coherent() with the smaller mask before doing calling any of the other DMA interfaces. However, if the bus is not capable of addressing the entire 32-bit range (as on some modern shmobile machines, or some of the really old machines), we need to limit the mask here already. Arnd