On 11/14/18 15:43, Philipp Zabel wrote:
> Hi Hans,
>
> On Tue, 2018-11-13 at 16:43 +0100, Hans Verkuil wrote:
>> Hi Philipp,
>>
>> On 11/13/18 16:06, Philipp Zabel wrote:
>>> From: John Sheu <sheu@xxxxxxxxxxxx>
>>>
>>> Videobuf2 presently does not allow VIDIOC_REQBUFS to destroy outstanding
>>> buffers if the queue is of type V4L2_MEMORY_MMAP, and if the buffers are
>>> considered "in use". This is different behavior than for other memory
>>> types and prevents us from deallocating buffers in following two cases:
>>>
>>> 1) There are outstanding mmap()ed views on the buffer. However even if
>>> we put the buffer in reqbufs(0), there will be remaining references,
>>> due to vma .open/close() adjusting vb2 buffer refcount appropriately.
>>> This means that the buffer will be in fact freed only when the last
>>> mmap()ed view is unmapped.
>>>
>>> 2) Buffer has been exported as a DMABUF. Refcount of the vb2 buffer
>>> is managed properly by VB2 DMABUF ops, i.e. incremented on DMABUF
>>> get and decremented on DMABUF release. This means that the buffer
>>> will be alive until all importers release it.
>>>
>>> Considering both cases above, there does not seem to be any need to
>>> prevent reqbufs(0) operation, because buffer lifetime is already
>>> properly managed by both mmap() and DMABUF code paths. Let's remove it
>>> and allow userspace freeing the queue (and potentially allocating a new
>>> one) even though old buffers might be still in processing.
>>>
>>> To let userspace know that the kernel now supports orphaning buffers
>>> that are still in use, add a new V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS
>>> to be set by reqbufs and create_bufs.
>>
>> Looks good, but I have some questions:
>>
>> 1) does v4l2-compliance together with vivid (easiest to test) still work?
>> I don't think I have a proper test for this in v4l2-compliance, but
>> I'm not 100% certain. If it fails with this patch, then please provide
>> a fix for v4l2-compliance as well.
>
> I have tested on v4.20-rc2 with 92539d3eda2c ("media: v4l: event: Add
> subscription to list before calling "add" operation") and this patch
> applied:
>
> $ modprobe vivid no_error_inj=1
> vivid-000: V4L2 capture device registered as video15
> vivid-000: V4L2 output device registered as video16
>
> $ v4l2-compliance -d 15 -s 1 --expbuf-device 16
> v4l2-compliance SHA: 98b4c9f276a18535b5691e5f350f59ffbf5a9aa5, 32 bits
> ...
> Total: 112, Succeeded: 112, Failed: 0, Warnings: 4
>
> The warnings are:
> warn: v4l2-test-formats.cpp(1426): doioctl(node, VIDIOC_CROPCAP, &cap)
Will be fixed when https://patchwork.linuxtv.org/patch/52811/ is merged.
> test Cropping: OK
> (one per input) and:
> warn: v4l2-test-controls.cpp(845): V4L2_CID_DV_RX_POWER_PRESENT not found for input 3
Waiting for a volunteer to teach vivid to properly emulate an HDMI connector.
So this looks good.
Will look at the v4l2-compliance patch tomorrow.
Regards,
Hans
> test VIDIOC_(UN)SUBSCRIBE_EVENT/DQEVENT: OK
>
>> 2) I would like to see a new test in v4l2-compliance for this: i.e. if
>> the capability is set, then check that you can call REQBUFS(0) before
>> unmapping all buffers. Ditto with dmabuffers.
>>
>> I said during the media summit that I wanted to be more strict about
>> requiring compliance tests before adding new features, so you're the
>> unlucky victim of that :-)
>
> That's fair. The SHA above is actually a lie, I had one patch applied.
>
> regards
> Philipp
>
