[PATCH 5/5] drm/tegra: Implement page-flipping support

[Thierry Reding]

On Wed, Jan 30, 2013 at 12:14:36PM +0100, Thierry Reding wrote:
> On Wed, Jan 30, 2013 at 11:42:40AM +0200, Ville Syrjälä wrote:
> > On Wed, Jan 30, 2013 at 10:32:47AM +0100, Thierry Reding wrote:
> > > On Wed, Jan 16, 2013 at 01:36:17PM +0100, Daniel Vetter wrote:
> > > > On Wed, Jan 16, 2013 at 11:01 AM, Thierry Reding
> > > > <thierry.reding at avionic-design.de> wrote:
> > > > > drm_events_release() should be enough to clean up the events, but I
> > > > > suspect the reason why Laurent put that code in was that the drm_crtc
> > > > > private data still has a reference to the event and needs to clear it.
> > > > > Otherwise the next page flip won't be scheduled because .page_flip()
> > > > > would return -EBUSY.
> > > > 
> > > > Hm, indeed we seem to have a nice bug in most drivers there :(
> > > 
> > > I think I may just recently have run into this bug on Intel hardware.
> > > Although perhaps I just used this wrongly.
> > > 
> > > Just for the fun of it I wanted to implement Conway's Game of Life on
> > > top of DRM/KMS. So I use two dumb buffer objects to alternately render
> > > to. Then I wanted to use page-flipping to synchronize with VBLANK.
> > > 
> > > So the sequence is basically:
> > > 
> > > 	while (!done) {
> > > 		grid_tick(grid);
> > > 		grid_draw(grid, screen);
> > > 		screen_flip(screen);
> > > 		grid_swap(grid);
> > > 	}
> > > 
> > > Where screen_flip() chooses the framebuffer and passes it to
> > > drmModePageFlip() like so:
> > > 
> > > 	int fb = screen->fb[screen->current];
> > > 
> > > 	drmModePageFlip(screen->fd, screen->crtc, fb,
> > > 			DRM_MODE_PAGE_FLIP_EVENT, screen);
> > > 
> > > This runs for about 3 seconds and then hangs, so the display is no
> > > longer updated. I've also verified that the same happens on Radeon.
> > > But maybe I am mistaken and this isn't the proper programming sequence?
> > 
> > You asked for page flip events. Do you actually handle them in your code?
> 
> Duh. No I wasn't =) I suppose some queue must be running full if the
> event isn't handled by calling drmHandleEvent(). Okay, this now works
> properly with page-flipping.

Just in case anybody's interested, the code is here:

	https://gitorious.org/thierryreding/kmslife

Thierry
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