2018-01-15 Hans Verkuil <hverkuil@xxxxxxxxx>: > On 01/15/2018 01:01 PM, Gustavo Padovan wrote: > > 2018-01-15 Alexandre Courbot <acourbot@xxxxxxxxxxxx>: > > > >> On Thu, Jan 11, 2018 at 1:07 AM, Gustavo Padovan <gustavo@xxxxxxxxxxx> wrote: > >>> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx> > >>> > >>> Explicit synchronization benefits a lot from ordered queues, they fit > >>> better in a pipeline with DRM for example so create a opt-in way for > >>> drivers notify videobuf2 that the queue is unordered. > >>> > >>> Drivers don't need implement it if the queue is ordered. > >> > >> This is going to make user-space believe that *all* vb2 drivers use > >> ordered queues by default, at least until non-ordered drivers catch up > >> with this change. Wouldn't it be less dangerous to do the opposite > >> (make queues non-ordered by default)? > > > > The rational behind this decision was because most formats/drivers are > > ordered so only a small amount of drivers need to changed. I think this > > was proposed by Hans on the Media Summit. > > > > I understand your concern. My question is how dangerous will it be. If > > you are building a product you will make the changes in the driver if > > they are not there yet, or if it is a distribution you'd never know > > which driver/format you are using so you should be prepared for > > everything. > > > > AFAIK all Capture drivers are ordered and that is where I think fences > > is most useful. > > Right. What could be done is to mark all codec drivers as unordered initially > ask the driver authors to verify this. All capture drivers using vb2 and not > using REQUEUE are ordered. That is a good way out. > > One thing we haven't looked at is what to do with drivers that do not use vb2. > Those won't support fences, but how will userspace know that fences are not > supported? I'm not sure what the best method is for that. > > I am leaning towards a new capability since this has to be advertised clearly. The capability flag makes sense to me, I'll incorporate it as part of my next patchset. Gustavo
