On 06/17/2016 12:10 AM, Hans Verkuil wrote:
On 06/16/2016 07:02 PM, Steve Longerbeam wrote:
On 06/16/2016 02:49 AM, Jack Mitchell wrote:
On 16/06/16 02:37, Steve Longerbeam wrote:
Hi Jack,
On 06/15/2016 03:43 AM, Jack Mitchell wrote:
<snip>
Trying to use a user pointer rather than mmap also fails and causes a kernel splat.
Hmm, I've tested userptr with the mem2mem driver, but maybe never
with video capture. I tried "v4l2-ctl -d/dev/video0 --stream-user=8" but
that returns "VIDIOC_QBUF: failed: Invalid argument", haven't tracked
down why (could be a bug in v4l2-ctl). Can you share the splat?
On re-checking the splat was the same v4l_cropcap that was mentioned before so I don't think it's related. The error I get back is:
VIDIOC_QBUF error 22, Invalid argument
I'm using the example program the the v4l2 docs [1].
I found the cause at least in my case. After enabling dynamic debug in
videobuf2-dma-contig.c, "v4l2-ctl -d/dev/video0 --stream-user=8" gives
me
[ 468.826046] user data must be aligned to 64 bytes
But even getting past that alignment issue, I've only tested userptr (in mem2mem
driver) by giving the driver a user address of a mmap'ed kernel contiguous
buffer. A true discontiguous user buffer may not work, the IPU DMA does not
support scatter-gather.
I don't think VB2_USERPTR should be enabled in this case due to the DMA limitations.
It won't allow you to use malloc()ed memory and the hack that allows you to pass
contiguous memory is superseded by the DMABUF mode.
Hi Hans, yes, I was going to suggest that. I will remove USERPTR
from both capture and mem2mem io_modes flags. Although I can
see where userptr support is still useful, that is for legacy middleware
that are still using mmap'ed userptrs and have not yet converted to
passing around dmabuf fd's.
But I've been perplexed for while on this, why vb2_dc_get_userptr()
resorts to
scatter-gather (when the given user buffer is found not to have valid
pfn's).
Shouldn't it be assumed that driver users of the vb2 dma-contig allocator
only support contiguous dma as the name implies? Maybe the issue is that
users that set VB2_USERPTR are implying they support scatter/gather, but
users of vb2-dma-contig could also be implying they do not, and would be
using vb2-dma-sg if that were the case.
Steve
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