Hi Mauro, 2017-06-30 Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>: > Em Fri, 16 Jun 2017 16:39:03 +0900 > Gustavo Padovan <gustavo@xxxxxxxxxxx> escreveu: > > > From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx> > > > > Hi, > > > > This adds support for Explicit Synchronization of shared buffers in V4L2. > > It uses the Sync File Framework[1] as vector to communicate the fences > > between kernel and userspace. > > > > Explicit Synchronization allows us to control the synchronization of > > shared buffers from userspace by passing fences to the kernel and/or > > receiving them from the the kernel. > > > > Fences passed to the kernel are named in-fences and the kernel should wait > > them to signal before using the buffer. On the other side, the kernel creates > > out-fences for every buffer it receives from userspace. This fence is sent back > > to userspace and it will signal when the capture, for example, has finished. > > > > Signalling an out-fence in V4L2 would mean that the job on the buffer is done > > and the buffer can be used by other drivers. > > > > The first patch proposes an userspace API for fences, then on patch 2 > > we prepare to the addition of in-fences in patch 3, by introducing the > > infrastructure on vb2 to wait on an in-fence signal before queueing the buffer > > in the driver. > > > > Patch 4 fix uvc v4l2 event handling and patch 5 configure q->dev for vivid > > drivers to enable to subscribe and dequeue events on it. > > > > Patches 6-7 enables support to notify BUF_QUEUED events, i.e., let userspace > > know that particular buffer was enqueued in the driver. This is needed, > > because we return the out-fence fd as an out argument in QBUF, but at the time > > it returns we don't know to which buffer the fence will be attached thus > > the BUF_QUEUED event tells which buffer is associated to the fence received in > > QBUF by userspace. > > > > Patches 8-9 add support to mark queues as ordered. Finally patches 10 and 11 > > add more fence infrastructure to support out-fences and finally patch 12 adds > > support to out-fences. > > > > Changelog are detailed in each patch. > > > > Please review! Thanks. > > Just reviewed the series. Most patches look good. > > I have one additional concern: if the changes here won't cause any > bad behaviors if fences is not available for some VB2 non V4L2 client. > I'm actually thinking on this: > > https://patchwork.linuxtv.org/patch/31613/ > > From what I saw, after this patch series, someone could try to > inconditionally open an out fences fd for a driver. Maybe this > should be denied by default, enabling such feature only if the > VB2 "client" (e. g. videobuf-v4l2) supports it. Yes, I think we can just reject the request if this non-VB2 client tries to use the arg flags for fences. Gustavo
