Hi Divneil,
On Mon, Apr 7, 2014 at 6:56 PM, Divneil Wadhawan <divneil@xxxxxxxxxxx> wrote:
> Hi,
>
> I have a V4L2 capture driver accepting a malloc'ed buffer.
> The driver is using vb2_vmalloc_memops (../drivers/media/v4l2-core/videobuf2-vmalloc.c) for user-space to kvaddr translation.
> Randomly, corrupted data is received by user-app.
>
> So, the question is regarding the handling of get_userptr, put_userptr by v4l2-core:
>
> const struct vb2_mem_ops vb2_vmalloc_memops = {
> ........
> .get_userptr = vb2_vmalloc_get_userptr, (get_user_pages() and vm_map_ram())
> .put_userptr = vb2_vmalloc_put_userptr, (set_page_dirty_lock() and put_page())
> .....
> };
>
> The driver prepares for the transaction by virtue of v4l2-core calling get_userptr (QBUF)
> After data is filled, driver puts on a done list (DQBUF)
>
> We never mark the pages as dirty (or put_userptr) after a transaction is complete.
> Here, in v4l2 core (videobuf2-core.c) , we conditionally put_userptr - when a QBUF with a different userptr on same index, or releasing buffers.
>
> Is it correct? Probably seems to be the reason for corrupted data.
This is an optimization and requires the mapping of userspace buffer
to v4l2_buffer index to not change.
Is it possible that your userspace is not always queuing the same
userptr memory areas with the same v4l2_buffer index values?
In other words, if you have 2 buffers in use, under userspace mapping
at addr1 and addr2, if you queue addr1 with index=0 and addr2 with
index=1 initially,
you should always keep queuing addr1 with index=0 and never 1, etc.
Also, what architecture are you running this on?
> Regards,
> Divneil --
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--
Best regards,
Pawel Osciak
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