From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mailout2.w1.samsung.com ([210.118.77.12]:8724 "EHLO mailout2.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752109Ab2FFL4s (ORCPT ); Wed, 6 Jun 2012 07:56:48 -0400 Received: from eusync4.samsung.com (mailout2.w1.samsung.com [210.118.77.12]) by mailout2.w1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0M57005I52JH8G90@mailout2.w1.samsung.com> for linux-media@vger.kernel.org; Wed, 06 Jun 2012 12:57:17 +0100 (BST) Received: from [106.116.48.223] by eusync4.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTPA id <0M57003IN2ILUW70@eusync4.samsung.com> for linux-media@vger.kernel.org; Wed, 06 Jun 2012 12:56:46 +0100 (BST) Message-id: <4FCF457A.9000201@samsung.com> Date: Wed, 06 Jun 2012 13:56:42 +0200 From: Tomasz Stanislawski MIME-version: 1.0 To: Laurent Pinchart Cc: linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, airlied@redhat.com, m.szyprowski@samsung.com, kyungmin.park@samsung.com, sumit.semwal@ti.com, daeinki@gmail.com, daniel.vetter@ffwll.ch, robdclark@gmail.com, pawel@osciak.com, linaro-mm-sig@lists.linaro.org, hverkuil@xs4all.nl, remi@remlab.net, subashrp@gmail.com, mchehab@redhat.com, g.liakhovetski@gmx.de Subject: Re: [PATCH 04/12] v4l: vb2-dma-contig: add setup of sglist for MMAP buffers References: <1337778455-27912-1-git-send-email-t.stanislaws@samsung.com> <1337778455-27912-5-git-send-email-t.stanislaws@samsung.com> <2101386.6sj5B2hAyl@avalon> In-reply-to: <2101386.6sj5B2hAyl@avalon> Content-type: text/plain; charset=ISO-8859-1 Content-transfer-encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi Laurent, Thank your for your comments. On 06/06/2012 10:06 AM, Laurent Pinchart wrote: > Hi Tomasz, > > Thanks for the patch. > > On Wednesday 23 May 2012 15:07:27 Tomasz Stanislawski wrote: >> This patch adds the setup of sglist list for MMAP buffers. >> It is needed for buffer exporting via DMABUF mechanism. >> >> Signed-off-by: Tomasz Stanislawski >> Signed-off-by: Kyungmin Park >> --- >> drivers/media/video/videobuf2-dma-contig.c | 70 ++++++++++++++++++++++++- >> 1 file changed, 68 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/media/video/videobuf2-dma-contig.c >> b/drivers/media/video/videobuf2-dma-contig.c index 52b4f59..ae656be 100644 >> --- a/drivers/media/video/videobuf2-dma-contig.c >> +++ b/drivers/media/video/videobuf2-dma-contig.c >> @@ -32,6 +32,7 @@ struct vb2_dc_buf { >> /* MMAP related */ >> struct vb2_vmarea_handler handler; >> atomic_t refcount; >> + struct sg_table *sgt_base; >> >> /* USERPTR related */ >> struct vm_area_struct *vma; >> @@ -189,14 +190,37 @@ static void vb2_dc_put(void *buf_priv) >> if (!atomic_dec_and_test(&buf->refcount)) >> return; >> >> + vb2_dc_release_sgtable(buf->sgt_base); >> dma_free_coherent(buf->dev, buf->size, buf->vaddr, buf->dma_addr); >> kfree(buf); >> } >> >> +static int vb2_dc_kaddr_to_pages(unsigned long kaddr, >> + struct page **pages, unsigned int n_pages) >> +{ >> + unsigned int i; >> + unsigned long pfn; >> + struct vm_area_struct vma = { >> + .vm_flags = VM_IO | VM_PFNMAP, >> + .vm_mm = current->mm, >> + }; >> + >> + for (i = 0; i < n_pages; ++i, kaddr += PAGE_SIZE) { > > The follow_pfn() kerneldoc mentions that it looks up a PFN for a user address. > The only users I've found in the kernel sources pass a user address. Is it > legal to use it for kernel addresses ? > It is not completely legal :). As I understand the mm code, the follow_pfn works only for IO/PFN mappings. This is the typical case (every case?) of mappings created by dma_alloc_coherent. In order to make this function work for a kernel pointer, one has to create an artificial VMA that has IO/PFN bits on. This solution is a hack-around for dma_get_pages (aka dma_get_sgtable). This way the dependency on dma_get_pages was broken giving a small hope of merging vb2 exporting. Marek prepared a patchset 'ARM: DMA-mapping: new extensions for buffer sharing' that adds dma buffers with no kernel mappings and dma_get_sgtable function. However this patchset is still in a RFC state. I have prepared a patch that removes vb2_dc_kaddr_to_pages and substitutes it with dma_get_pages. It will become a part of vb2-exporter patches just after dma_get_sgtable is merged (or at least acked by major maintainers). >> + if (follow_pfn(&vma, kaddr, &pfn)) >> + break; >> + pages[i] = pfn_to_page(pfn); >> + } >> + >> + return i; >> +} >> + >> static void *vb2_dc_alloc(void *alloc_ctx, unsigned long size) >> { >> struct device *dev = alloc_ctx; >> struct vb2_dc_buf *buf; >> + int ret = -ENOMEM; >> + int n_pages; >> + struct page **pages = NULL; >> >> buf = kzalloc(sizeof *buf, GFP_KERNEL); >> if (!buf) >> @@ -205,10 +229,41 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned >> long size) buf->vaddr = dma_alloc_coherent(dev, size, &buf->dma_addr, >> GFP_KERNEL); if (!buf->vaddr) { >> dev_err(dev, "dma_alloc_coherent of size %ld failed\n", size); >> - kfree(buf); >> - return ERR_PTR(-ENOMEM); >> + goto fail_buf; >> + } >> + >> + WARN_ON((unsigned long)buf->vaddr & ~PAGE_MASK); >> + WARN_ON(buf->dma_addr & ~PAGE_MASK); >> + >> + n_pages = PAGE_ALIGN(size) >> PAGE_SHIFT; >> + >> + pages = kmalloc(n_pages * sizeof pages[0], GFP_KERNEL); >> + if (!pages) { >> + dev_err(dev, "failed to alloc page table\n"); >> + goto fail_dma; >> + } >> + >> + ret = vb2_dc_kaddr_to_pages((unsigned long)buf->vaddr, pages, n_pages); >> + if (ret < 0) { >> + dev_err(dev, "failed to get buffer pages from DMA API\n"); >> + goto fail_pages; >> + } >> + if (ret != n_pages) { >> + ret = -EFAULT; >> + dev_err(dev, "failed to get all pages from DMA API\n"); >> + goto fail_pages; >> + } >> + >> + buf->sgt_base = vb2_dc_pages_to_sgt(pages, n_pages, 0, size); >> + if (IS_ERR(buf->sgt_base)) { >> + ret = PTR_ERR(buf->sgt_base); >> + dev_err(dev, "failed to prepare sg table\n"); >> + goto fail_pages; >> } >> >> + /* pages are no longer needed */ >> + kfree(pages); >> + >> buf->dev = dev; >> buf->size = size; >> >> @@ -219,6 +274,17 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned >> long size) atomic_inc(&buf->refcount); >> >> return buf; >> + >> +fail_pages: >> + kfree(pages); >> + >> +fail_dma: > > You can merge the fail_pages and fail_dma labels, as kfree(NULL) is valid. > Yes, I can. But there are two reasons for not doing that: - first: calling a dummy kfree introduces a negligible but non-zero overhead - second: the fail-path becomes more difficult to understand Regards, Tomasz Stanislawski >> + dma_free_coherent(dev, size, buf->vaddr, buf->dma_addr); >> + >> +fail_buf: >> + kfree(buf); >> + >> + return ERR_PTR(ret); >> } >> >> static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma) >