[RFC] drm: add flip-work helper

[Daniel Vetter]

On Sun, Aug 04, 2013 at 10:20:54PM -0400, Rob Clark wrote:
> On Sun, Aug 4, 2013 at 1:34 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Thu, Aug 1, 2013 at 1:23 AM, Rob Clark <robdclark at gmail.com> wrote:
> >> A small helper to queue up work to do, from workqueue context, after a
> >> flip.  Typically useful to defer unreffing buffers that may be read by
> >> the display controller until vblank.
> >>
> >> Signed-off-by: Rob Clark <robdclark at gmail.com>
> >> ---
> >> I've re-inventing the same wheel three times in as many drivers (omapdrm,
> >> tilcdc, and in upcoming msm driver I need two of 'em).  I guess it is
> >> time to helper-up.
> >>
> >> I'll update omapdrm and tilcdc to use this as well, but I figured I'd
> >> send an RFC first in case anyone wants to get their bikeshed on.  If
> >> there are other drivers that could use this, and are straightforward
> >> to convert over, let me know and I can update them as well.
> >
> >
> > One thing drm/i915 needs is to be able to flush the workqueue (to make
> > sure we don't pile up giant amounts of buffers waiting to be unpinned
> > and so temporarily leak a bit of memory). So some way to synchronously
> > flush out flip functions would be required (and make sure all that
> > have been queued up to that point are really completed). But at that
> > point a separate workqueue sounds simpler, so I wonder a bit what this
> > gains us? At roughly 50Hz flip work functions aren't really that
> > performance critical imo ...
> 
> you could of course do separate or same workqueue from your main
> render-complete workqueue, or flush the workqueue at whatever point
> you want..  I suppose if you are queuing from a context that is safe
> to sleep you could have a blocking-queue function.  I haven't really
> needed anything like that so far, but feel free to extend the
> flip-work helper however you need to be useful for i915.  (Or point me
> at the bits in i915 that do something similar and I'll have a think
> about how to convert that)

queue_work in do_intel_finish_page_flip and flush_work in
intel_crtc_page_flip is the relevant code. The former is called from irq
context.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch