[lkml]   [2018]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v7 1/6] [media] vb2: add is_unordered callback for drivers
2018-01-15 Hans Verkuil <>:

> On 01/15/2018 01:01 PM, Gustavo Padovan wrote:
> > 2018-01-15 Alexandre Courbot <>:
> >
> >> On Thu, Jan 11, 2018 at 1:07 AM, Gustavo Padovan <> wrote:
> >>> From: Gustavo Padovan <>
> >>>
> >>> 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.


 \ /
  Last update: 2018-01-15 18:56    [W:0.153 / U:2.832 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site