From patchwork Thu Jan 12 18:07:26 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Robin Murphy X-Patchwork-Id: 9513779 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 363F660476 for ; Thu, 12 Jan 2017 18:08:00 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 2B087286E4 for ; Thu, 12 Jan 2017 18:08:00 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1BC20286FA; Thu, 12 Jan 2017 18:08:00 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 8474D286E4 for ; Thu, 12 Jan 2017 18:07:59 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1cRjn1-00084v-Js; Thu, 12 Jan 2017 18:07:55 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1cRjmv-00083u-U6 for linux-arm-kernel@lists.infradead.org; Thu, 12 Jan 2017 18:07:53 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 08B4EAD7; Thu, 12 Jan 2017 10:07:29 -0800 (PST) Received: from [10.1.211.71] (e104324-lin.cambridge.arm.com [10.1.211.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A2FA33F24D; Thu, 12 Jan 2017 10:07:27 -0800 (PST) Subject: Re: [RFC PATCH v4 0/5] ARM: Fix dma_alloc_coherent() and friends for NOMMU To: Vladimir Murzin , Benjamin Gaignard References: <1484057925-23586-1-git-send-email-vladimir.murzin@arm.com> <1908ef72-beb0-1855-3c49-d5a37f014c17@arm.com> <78458e5f-6b30-ab9b-1226-83fe3a844e3a@arm.com> From: Robin Murphy Message-ID: <8a428278-fe0f-ca1f-2b6a-96fdbb363db4@arm.com> Date: Thu, 12 Jan 2017 18:07:26 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <78458e5f-6b30-ab9b-1226-83fe3a844e3a@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20170112_100750_098582_DFC592EB X-CRM114-Status: GOOD ( 27.17 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: sza@esh.hu, Alexandre Torgue , linux@armlinux.org.uk, kbuild-all@01.org, linux-arm-kernel@lists.infradead.org, Marek Szyprowski Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP On 12/01/17 17:15, Vladimir Murzin wrote: > On 12/01/17 17:04, Robin Murphy wrote: >> On 12/01/17 16:52, Vladimir Murzin wrote: >>> On 12/01/17 10:55, Benjamin Gaignard wrote: >>>> 2017-01-12 11:35 GMT+01:00 Benjamin Gaignard : >>>>> 2017-01-11 15:34 GMT+01:00 Vladimir Murzin : >>>>>> On 11/01/17 13:17, Benjamin Gaignard wrote: >>>>>>> 2017-01-10 15:18 GMT+01:00 Vladimir Murzin : >>>>>>>> Hi, >>>>>>>> >>>>>>>> It seem that addition of cache support for M-class cpus uncovered >>>>>>>> latent bug in DMA usage. NOMMU memory model has been treated as being >>>>>>>> always consistent; however, for R/M classes of cpu memory can be >>>>>>>> covered by MPU which in turn might configure RAM as Normal >>>>>>>> i.e. bufferable and cacheable. It breaks dma_alloc_coherent() and >>>>>>>> friends, since data can stuck in caches now or be buffered. >>>>>>>> >>>>>>>> This patch set is trying to address the issue by providing region of >>>>>>>> memory suitable for consistent DMA operations. It is supposed that >>>>>>>> such region is marked by MPU as non-cacheable. Robin suggested to >>>>>>>> advertise such memory as reserved shared-dma-pool, rather then using >>>>>>>> homebrew command line option, and extend dma-coherent to provide >>>>>>>> default DMA area in the similar way as it is done for CMA (PATCH >>>>>>>> 2/5). It allows us to offload all bookkeeping on generic coherent DMA >>>>>>>> framework, and it is seems that it might be reused by other >>>>>>>> architectures like c6x and blackfin. >>>>>>>> >>>>>>>> Dedicated DMA region is required for cases other than: >>>>>>>> - MMU/MPU is off >>>>>>>> - cpu is v7m w/o cache support >>>>>>>> - device is coherent >>>>>>>> >>>>>>>> In case one of the above conditions is true dma operations are forced >>>>>>>> to be coherent and wired with dma_noop_ops. >>>>>>>> >>>>>>>> To make life easier NOMMU dma operations are kept in separate >>>>>>>> compilation unit. >>>>>>>> >>>>>>>> Since the issue was reported in the same time as Benjamin sent his >>>>>>>> patch [1] to allow mmap for NOMMU, his case is also addressed in this >>>>>>>> series (PATCH 1/5 and PATCH 3/5). >>>>>>>> >>>>>>>> Thanks! >>>>>>> >>>>>>> I have tested this v4 on my setup (stm32f4, no cache, no MPU) and unfortunately >>>>>>> it doesn't work with my drm/kms driver. >>>>>> >>>>>> I guess the same is for fbmem, but would be better to have confirmation since >>>>>> amba-clcd I use has not been ported to drm/kms (yet), so I can't test. >>>>>> >>>>>>> I haven't any errors but nothing is displayed unlike what I have when >>>>>>> using current dma-mapping >>>>>>> code. >>>>>>> I guess the issue is coming from dma-noop where __get_free_pages() is >>>>>>> used instead of alloc_pages() >>>>>>> in dma-mapping. >>>>>> >>>>>> Unless I've missed something bellow is a call stack for both >>>>>> >>>>>> #1 >>>>>> __alloc_simple_buffer >>>>>> __dma_alloc_buffer >>>>>> alloc_pages >>>>>> split_page >>>>>> __dma_clear_buffer >>>>>> memset >>>>>> page_address >>>>>> >>>>>> #2 >>>>>> __get_free_pages >>>>>> alloc_pages >>>>>> page_address >>>>>> >>>>>> So the difference is that nommu case in dma-mapping.c memzeros memory, handles >>>>>> DMA_ATTR_NO_KERNEL_MAPPING and does optimisation of memory usage. >>>>>> >>>>>> Is something from above critical for your driver? >>>>> >>>>> I have removed all the diff (split_page, __dma_clear_buffer, memset) >>>>> from #1 and it is still working. >>>>> DMA_ATTR_NO_KERNEL_MAPPING flag is not set when allocating the buffer. >>>>> >>>>> I have investigated more and found that dma-noop doesn't take care of >>>>> "dma-ranges" property which is set in DT. >>>>> I believed that is the root cause of my problem with your patches. >>>> >>>> After testing changing virt_to_phys to virt_to_dma in dma-noop.c fix the issue >>>> modetest and fbdemo are now still functional. >>>> >>> >>> Thanks for narrowing it down! I did not noticed that stm32f4 remap its memory, >>> so dma-ranges property is in use. >>> >>> It looks like virt_to_dma is ARM specific, so I probably have to discard idea >>> of reusing dma-noop-ops and switch logic into dma-mapping-nommu.c based on >>> is_device_dma_coherent(dev) check. >> >> dma_pfn_offset is a member of struct device, so it should be OK for >> dma_noop_ops to also make reference to it (and assume it's zero if not >> explicitly set). >> >>> Meanwhile, I'm quite puzzled on how such memory remaping should work together >>> with reserved memory. It seem it doesn't account dma-ranges while reserving >>> memory (it is too early) nor while allocating/mapping/etc. >> >> The reserved memory is described in terms of CPU physical addresses, so >> a device offset shouldn't matter from that perspective. It only comes >> into play at the point you generate the dma_addr_t to hand off to the >> device - only then do you need to transform the CPU physical address of >> the allocated/mapped page into the device's view of that page (i.e. >> subtract the offset). > > Thanks for explanation! So dma-coherent.c should be modified, right? I see > that some architectures provide phys_to_dma/dma_to_phys helpers primary for > swiotlb, is it safe to reuse them given that default implementation is > provided? Nothing under Documentation explains how they supposed to be used, > sorry if asking stupid question. Those are essentially SWIOTLB-specific, so can't be universally relied upon. I think something like this ought to suffice: ---8<--- @@ -32,7 +37,7 @@ static dma_addr_t dma_noop_map_page(struct device *dev, struct page *page, enum dma_data_direction dir, unsigned long attrs) { - return page_to_phys(page) + offset; + return page_to_phys(page) + offset - dma_noop_dev_offset(dev); } static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nents, @@ -47,7 +52,8 @@ static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nent BUG_ON(!sg_page(sg)); va = sg_virt(sg); - sg_dma_address(sg) = (dma_addr_t)virt_to_phys(va); + sg_dma_address(sg) = (dma_addr_t)virt_to_phys(va) - + dma_noop_dev_offset(dev); sg_dma_len(sg) = sg->length; } --->8--- intentionally whitespace-damaged by copy-pasting off my terminal to emphasise how utterly untested it is ;) Robin. diff --git a/lib/dma-noop.c b/lib/dma-noop.c index 3d766e78fbe2..fbb1b37750d5 100644 --- a/lib/dma-noop.c +++ b/lib/dma-noop.c @@ -8,6 +8,11 @@ #include #include +static dma_addr_t dma_noop_dev_offset(struct device *dev) +{ + return (dma_addr_t)dev->dma_pfn_offset << PAGE_SHIFT; +} + static void *dma_noop_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs) @@ -16,7 +21,7 @@ static void *dma_noop_alloc(struct device *dev, size_t size, ret = (void *)__get_free_pages(gfp, get_order(size)); if (ret) - *dma_handle = virt_to_phys(ret); + *dma_handle = virt_to_phys(ret) - dma_noop_dev_offset(dev); return ret; }