From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754920Ab1B1PRm (ORCPT ); Mon, 28 Feb 2011 10:17:42 -0500 Received: from perceval.ideasonboard.com ([95.142.166.194]:36971 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754901Ab1B1PRk (ORCPT ); Mon, 28 Feb 2011 10:17:40 -0500 From: Laurent Pinchart To: Jiri Slaby Subject: Re: [PATCH v2 -resend#1 1/1] V4L: videobuf, don't use dma addr as physical Date: Mon, 28 Feb 2011 16:14:51 +0100 User-Agent: KMail/1.13.6 (Linux/2.6.37-gentoo; KDE/4.6.0; x86_64; ; ) Cc: mchehab@infradead.org, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, jirislaby@gmail.com, Konrad Rzeszutek Wilk References: <1298885822-10083-1-git-send-email-jslaby@suse.cz> <201102281153.30585.laurent.pinchart@ideasonboard.com> <4D6BBA3F.2000205@suse.cz> In-Reply-To: <4D6BBA3F.2000205@suse.cz> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Message-Id: <201102281615.02193.laurent.pinchart@ideasonboard.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jiri, On Monday 28 February 2011 16:07:43 Jiri Slaby wrote: > On 02/28/2011 11:53 AM, Laurent Pinchart wrote: > > On Monday 28 February 2011 10:37:02 Jiri Slaby wrote: > >> mem->dma_handle is a dma address obtained by dma_alloc_coherent which > >> needn't be a physical address in presence of IOMMU. So ensure we are > >> remapping (remap_pfn_range) the right page in __videobuf_mmap_mapper > >> by using virt_to_phys(mem->vaddr) and not mem->dma_handle. > > > > Quoting arch/arm/include/asm/memory.h, > > > > /* > > > > * These are *only* valid on the kernel direct mapped RAM memory. > > Which the DMA allocation shall be. > > > * Note: Drivers should NOT use these. > > This is weird. > > > They are the wrong > > > > * translation for translating DMA addresses. Use the driver > > * DMA support - see dma-mapping.h. > > Yes, ACK, and vice versa. DMA addresses cannot be used as physical ones. > > > */ > > > > static inline unsigned long virt_to_phys(const volatile void *x) > > { > > > > return __virt_to_phys((unsigned long)(x)); > > > > } > > > > Why would you use physically contiguous memory if you have an IOMMU > > anyway ? > > Sorry, what? When IOMMU is used, dma_alloc_* functions may return "tags" > as a DMA address, not a physical address. So using these DMA "addresses" > directly (e.g. in remap_pfn_range) is a bug. What I mean is that videobuf-dma-contig is meant to be used by drivers that require physically contiguous memory. If the system has an IOMMU, why would drivers need that ? > Maybe there is a better way to convert a kernel address of the DMA > mapping into a physical frame, but I'm not aware of any... > > >> While at it, use PFN_DOWN instead of explicit shift. > >> > >> Signed-off-by: Jiri Slaby > >> Cc: Mauro Carvalho Chehab > >> Cc: Konrad Rzeszutek Wilk > >> --- > >> > >> drivers/media/video/videobuf-dma-contig.c | 2 +- > >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> > >> diff --git a/drivers/media/video/videobuf-dma-contig.c > >> b/drivers/media/video/videobuf-dma-contig.c index c969111..19d3e4a > >> 100644 --- a/drivers/media/video/videobuf-dma-contig.c > >> +++ b/drivers/media/video/videobuf-dma-contig.c > >> @@ -300,7 +300,7 @@ static int __videobuf_mmap_mapper(struct > >> videobuf_queue *q, > >> > >> vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > >> retval = remap_pfn_range(vma, vma->vm_start, > >> > >> - mem->dma_handle >> PAGE_SHIFT, > >> + PFN_DOWN(virt_to_phys(mem->vaddr)) > >> > >> size, vma->vm_page_prot); > >> > >> if (retval) { > >> > >> dev_err(q->dev, "mmap: remap failed with error %d. ", retval); -- Regards, Laurent Pinchart