Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751519AbaLES3K (ORCPT ); Fri, 5 Dec 2014 13:29:10 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:45463 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750975AbaLES3I (ORCPT ); Fri, 5 Dec 2014 13:29:08 -0500 Date: Fri, 5 Dec 2014 18:28:51 +0000 From: Catalin Marinas To: Russell King - ARM Linux Cc: Hante Meuleman , linux-wireless , brcm80211-dev-list , "linux-kernel@vger.kernel.org" , Will Deacon , Arend Van Spriel , David Miller , "linux-arm-kernel@lists.infradead.org" , Marek Szyprowski Subject: Re: using DMA-API on ARM Message-ID: <20141205182851.GC31222@e104818-lin.cambridge.arm.com> References: <5481794E.4050406@broadcom.com> <20141205094507.GP11285@n2100.arm.linux.org.uk> <20141205122423.GK1630@arm.com> <20141205132332.GS11285@n2100.arm.linux.org.uk> <20141205150648.GT11285@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141205150648.GT11285@n2100.arm.linux.org.uk> 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, Dec 05, 2014 at 03:06:48PM +0000, Russell King - ARM Linux wrote: > I've been doing more digging into the current DMA code, and I'm dismayed > to see that there's new bugs in it... > > commit 513510ddba9650fc7da456eefeb0ead7632324f6 > Author: Laura Abbott > Date: Thu Oct 9 15:26:40 2014 -0700 > > common: dma-mapping: introduce common remapping functions > > This uses map_vm_area() to achieve the remapping of pages allocated inside > dma_alloc_coherent(). dma_alloc_coherent() is documented in a rather > round-about way in Documentation/DMA-API.txt: > > | Part Ia - Using large DMA-coherent buffers > | ------------------------------------------ > | > | void * > | dma_alloc_coherent(struct device *dev, size_t size, > | dma_addr_t *dma_handle, gfp_t flag) > | > | void > | dma_free_coherent(struct device *dev, size_t size, void *cpu_addr, > | dma_addr_t dma_handle) > | > | Free a region of consistent memory you previously allocated. dev, > | size and dma_handle must all be the same as those passed into > | dma_alloc_coherent(). cpu_addr must be the virtual address returned by > | the dma_alloc_coherent(). > | > | Note that unlike their sibling allocation calls, these routines > | may only be called with IRQs enabled. > > Note that very last paragraph. What this says is that it is explicitly > permitted to call dma_alloc_coherent() with IRQs disabled. This is solved by using a pre-allocated, pre-mapped atomic_pool which avoids any further mapping. __dma_alloc() calls __alloc_from_pool() when !__GFP_WAIT. This code got pretty complex and we may find bugs. It can be simplified by a pre-allocated non-cacheable region that is safe in atomic context (how big you allocate this is hard to say). > If the problem which you (Broadcom) are suffering from is down to the > issue I suspect (that being having mappings with different cache > attributes) then I'm not sure that there's anything we can realistically > do about that. There's a number of issues which make it hard to see a > way forward. I'm still puzzled by this problem, so I don't have any suggestion yet. I wouldn't blame the mismatched attributes yet as I haven't seen such problem in practice (but you never know). How does the DT describe this device? Could it have some dma-coherent property in there that causes dma_alloc_coherent() to create a cacheable memory? The reverse could also cause problems: the device is coherent but the CPU creates a non-cacheable mapping. -- Catalin -- 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/