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    SubjectRE: [PATCH] Video/UVC: Port mainlined uvc video driver to NOMMU
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    From


    >-----Original Message-----
    >From: Laurent Pinchart [mailto:laurent.pinchart@skynet.be]
    >Sent: Sunday, November 09, 2008 10:22 PM
    >To: Bryan Wu
    >Cc: linux-uvc-devel@lists.berlios.de; video4linux-list@redhat.com;
    linux-
    >kernel@vger.kernel.org; Michael Hennerich
    >Subject: Re: [PATCH] Video/UVC: Port mainlined uvc video driver to
    NOMMU
    >
    >Hi Bryan, Michael,
    >
    >On Thursday 06 November 2008, Bryan Wu wrote:
    >> From: Michael Hennerich <michael.hennerich@analog.com>
    >>
    >> Add NOMMU mmap support.
    >>
    >> Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
    >> Signed-off-by: Bryan Wu <cooloney@kernel.org>
    >> ---
    >> drivers/media/video/uvc/uvc_v4l2.c | 14 ++++++++++++++
    >> 1 files changed, 14 insertions(+), 0 deletions(-)
    >>
    >> diff --git a/drivers/media/video/uvc/uvc_v4l2.c
    >> b/drivers/media/video/uvc/uvc_v4l2.c index 758dfef..2237f5e 100644
    >> --- a/drivers/media/video/uvc/uvc_v4l2.c
    >> +++ b/drivers/media/video/uvc/uvc_v4l2.c
    >> @@ -1050,6 +1050,7 @@ static int uvc_v4l2_mmap(struct file *file,
    struct
    >> vm_area_struct *vma) break;
    >> }
    >>
    >> +#ifdef CONFIG_MMU
    >> if (i == video->queue.count || size != video->queue.buf_size) {
    >> ret = -EINVAL;
    >> goto done;
    >> @@ -1071,7 +1072,20 @@ static int uvc_v4l2_mmap(struct file *file,
    struct
    >> vm_area_struct *vma) addr += PAGE_SIZE;
    >> size -= PAGE_SIZE;
    >> }
    >> +#else
    >> + if (i == video->queue.count ||
    >> + PAGE_ALIGN(size) != video->queue.buf_size) {
    >
    >Just out of curiosity, why do you need to PAGE_ALIGN size for non-MMU
    >platforms ?

    Size and video->queue.buf_size is not the 100% same size (off by a few
    bytes < pagesize), I think it's because on NOMMU the kernel calls
    kmalloc() to allocate the buffer, not get_free_page().


    >
    >> + ret = -EINVAL;
    >> + goto done;
    >> + }
    >> +
    >> + vma->vm_flags |= VM_IO | VM_MAYSHARE; /*
    documentation/nommu-mmap.txt
    >*/
    >
    >VM_MAYSHARE is not documented anywhere in Documentation/ in Linux
    2.6.28-
    >rc3.
    >Why is it needed for non-MMU architectures only ?

    mmap on NOMMU is a bit tricky and very restricted.
    In case user does a MAP_SHARED with some combination of the PROT_###
    Flags the mmap fails. What's allowed and what's not is documented in
    documentation/nommu-mmap.txt
    Setting VM_MAYSHARE allows user MAP_PRIVATE mappings.

    -Michael

    >
    >> +
    >> + addr = (unsigned long)video->queue.mem + buffer->buf.m.offset;
    >>
    >> + vma->vm_start = addr;
    >> + vma->vm_end = addr + video->queue.buf_size;
    >> +#endif
    >> vma->vm_ops = &uvc_vm_ops;
    >> vma->vm_private_data = buffer;
    >> uvc_vm_open(vma);
    >
    >Best regards,
    >
    >Laurent Pinchart


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