From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Date: Mon, 09 Apr 2018 11:11:22 +0000 Subject: Re: [RFC v2 2/2] base: dma-mapping: Postpone page_to_pfn() on mmap() Message-Id: <7da3f31e-e4ad-7f1a-e66c-0d3e0fb8b27d@arm.com> List-Id: References: <1510679286-6988-1-git-send-email-jacopo+renesas@jmondi.org> <1510679286-6988-3-git-send-email-jacopo+renesas@jmondi.org> <20180409072547.GU20945@w540> In-Reply-To: <20180409072547.GU20945@w540> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: jacopo mondi Cc: dalias-8zAoT0mYgF4@public.gmane.org, ysato-Rn4VEauK+AKRv+LV9MX5uooqe+aC9MnS@public.gmane.org, linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-renesas-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org, laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org, Jacopo Mondi Hi Jacopo, On 09/04/18 08:25, jacopo mondi wrote: > Hi Robin, Laurent, > a long time passed, sorry about this. > > On Wed, Nov 15, 2017 at 01:38:23PM +0000, Robin Murphy wrote: >> On 14/11/17 17:08, Jacopo Mondi wrote: >>> On SH4 architecture, with SPARSEMEM memory model, translating page to >>> pfn hangs the CPU. Post-pone translation to pfn after >>> dma_mmap_from_dev_coherent() function call as it succeeds and make page >>> translation not necessary. >>> >>> This patch was suggested by Laurent Pinchart and he's working to submit >>> a proper fix mainline. Not sending for inclusion at the moment. >> >> Y'know, I think this patch does have some merit by itself - until we know >> that cpu_addr *doesn't* represent some device-private memory which is not >> guaranteed to be backed by a struct page, calling virt_to_page() on it is >> arguably semantically incorrect, even if it might happen to be benign in >> most cases. > > I still need to carry this patch in my trees to have a working dma memory mapping > on SH4 platforms. My understanding from your comment is that there may > be a way forward for this patch, do you still think the same? Have you > got any suggestion on how to improve this eventually for inclusion? As before, the change itself does seem reasonable; it might be worth rewording the commit message in more general terms rather than making it sound like an SH-specific workaround (which I really don't think it is), but otherwise I'd say just repost it as a non-RFC patch. Robin. > > Thanks > j > >> >> Robin. >> >>> Suggested-by: Laurent Pinchart >>> Signed-off-by: Jacopo Mondi >>> --- >>> drivers/base/dma-mapping.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c >>> index e584edd..73d64d3 100644 >>> --- a/drivers/base/dma-mapping.c >>> +++ b/drivers/base/dma-mapping.c >>> @@ -227,8 +227,8 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma, >>> #ifndef CONFIG_ARCH_NO_COHERENT_DMA_MMAP >>> unsigned long user_count = vma_pages(vma); >>> unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT; >>> - unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr)); >>> unsigned long off = vma->vm_pgoff; >>> + unsigned long pfn; >>> >>> vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); >>> >>> @@ -236,6 +236,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma, >>> return ret; >>> >>> if (off < count && user_count <= (count - off)) { >>> + pfn = page_to_pfn(virt_to_page(cpu_addr)); >>> ret = remap_pfn_range(vma, vma->vm_start, >>> pfn + off, >>> user_count << PAGE_SHIFT, >>> -- >>> 2.7.4 >>> >>> _______________________________________________ >>> iommu mailing list >>> iommu@lists.linux-foundation.org >>> https://lists.linuxfoundation.org/mailman/listinfo/iommu >>>