From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751368AbaKUSJh (ORCPT ); Fri, 21 Nov 2014 13:09:37 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:36959 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750752AbaKUSJg (ORCPT ); Fri, 21 Nov 2014 13:09:36 -0500 Date: Fri, 21 Nov 2014 18:09:25 +0000 From: Catalin Marinas To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Will Deacon , "linux-kernel@vger.kernel.org" , Ding Tianhong Subject: Re: For the problem when using swiotlb Message-ID: <20141121180925.GG19783@e104818-lin.cambridge.arm.com> References: <5469E26B.2010905@huawei.com> <5029442.vhLMp7Ns7F@wuerfel> <20141121165708.GF19783@e104818-lin.cambridge.arm.com> <2530749.roRsteyaXx@wuerfel> <20141121175118.GA10451@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141121175118.GA10451@localhost> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 21, 2014 at 05:51:19PM +0000, Catalin Marinas wrote: > On Fri, Nov 21, 2014 at 05:04:28PM +0000, Arnd Bergmann wrote: > > On Friday 21 November 2014 16:57:09 Catalin Marinas wrote: > > > There is a scenario where smaller mask would work on arm64. For example > > > Juno, you can have 2GB of RAM in the 32-bit phys range (starting at > > > 0x80000000). A device with 31-bit mask and a dma_pfn_offset of > > > 0x80000000 would still work (there isn't any but just as an example). So > > > the check in dma_alloc_coherent() would be something like: > > > > > > phys_to_dma(top of ZONE_DMA) - dma_pfn_offset <= coherent_dma_mask > > > > > > (or assuming RAM starts at 0 and ignoring dma_pfn_offset for now) > > > > > > If the condition above fails, dma_alloc_coherent() would no longer fall > > > back to swiotlb but issue a dev_warn() and return NULL. > > > > Ah, that looks like it should work on all architectures, very nice. > > How about checking this condition, and then printing a small warning > > (dev_warn, not WARN_ON) and setting the dma_mask pointer to NULL? > > I would not add the above ZONE_DMA check to of_dma_configure(). For > example on arm64, we may not support a small coherent_dma_mask but the > same value for dma_mask could be fine via swiotlb bouncing (or IOMMU). > However, that's an arch-specific decision. Maybe after the above setting > of dev->coherent_dma_mask in of_dma_configure(), we could add: > > if (!dma_supported(dev, dev->coherent_dma_mask)) > dev->dma_mask = NULL; > > The arch dma_supported() can check the swiotlb bouncing or ZONE_DMA > limits. More precisely, that's what I meant: diff --git a/drivers/of/platform.c b/drivers/of/platform.c index 3b64d0bf5bba..4fcdfed6a6df 100644 --- a/drivers/of/platform.c +++ b/drivers/of/platform.c @@ -172,13 +172,6 @@ static void of_dma_configure(struct device *dev) dev->coherent_dma_mask = DMA_BIT_MASK(32); /* - * Set it to coherent_dma_mask by default if the architecture - * code has not set it. - */ - if (!dev->dma_mask) - dev->dma_mask = &dev->coherent_dma_mask; - - /* * if dma-coherent property exist, call arch hook to setup * dma coherent operations. */ @@ -188,18 +181,32 @@ static void of_dma_configure(struct device *dev) } /* - * if dma-ranges property doesn't exist - just return else - * setup the dma offset + * If dma-ranges property exists - setup the dma offset. */ ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size); if (ret < 0) { dev_dbg(dev, "no dma range information to setup\n"); - return; + size = 0; + } else { + /* 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); } - /* 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); + /* + * If the bus dma-ranges property specifies a size smaller than 4GB, + * the device would not be capable of accessing the whole 32-bit + * space, so reduce the default coherent_dma_mask accordingly. + */ + if (size && size < (1ULL << 32)) + dev->coherent_dma_mask = DMA_BIT_MASK(ilog2(size)); + + /* + * Set dma_mask to coherent_dma_mask by default if the architecture + * code has not set it and DMA on such mask is supported. + */ + if (!dev->dma_mask && dma_supported(dev, dev->coherent_dma_mask)) + dev->dma_mask = &dev->coherent_dma_mask; } /** -- Catalin