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

[Thierry Reding]

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This runs for about 3 seconds and then hangs, so the display is no
longer updated.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?

Thierry
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 836 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/dri-devel/attachments/20130130/7794ee9c/attachment.pgp>