On 11/15/2018 08:49 AM, Laurent Pinchart wrote: > Hi Hans, > > > On Thursday, 15 November 2018 09:30:55 EET Hans Verkuil wrote: >> On 11/14/2018 08:52 PM, Laurent Pinchart wrote: >>> On Tuesday, 13 November 2018 17:43:48 EET Hans Verkuil wrote: >>>> 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. >>>> >>>> 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 :-) >>> >>> Do you have plans to refactor and document the v4l2-compliance internals >>> to make it easier ? >> >> Yes. I hope to be able to set aside one or two days for that in the next two >> weeks. > > That would be great ! Let me know if you would like to discuss how the code > base could be refactored. > I'm happy to hear your ideas, but I only have one day for refactoring, so it is very limited what can be done. Frankly, it is mainly v4l2-test-buffers.cpp that I would like to split up in two parts: one for the tests that do not require actual streaming and one part for all the streaming tests. Documentation (esp. cv4l-helpers.h which is used a lot) is much more important and I wanted to spend the second day on that. Regards, Hans
