On Mon, 30 Mar 2009 01:10:51 -0500
Robert Noland <rnol...@2hip.net> wrote:
> The Intel driver continues to call modeset before installing the irq
> handler. I discussed this issue several months ago, but have only
> recently become painfully aware of the deeper issues. Things seem to
> work ok, when you first start X, due to the fact that nothing is
> actually waiting on vblanks before the handler gets installed.
> During a Vt switch however, what I found was that with gears running
> synced to vblank while switching, pre-modeset says that vblanks are
> on and enables the pipestat registers. post-modeset schedules them
> to be disabled at some point in the future. At this point,
> vblank_enabled = 1. Now, the interrupt handler gets installed, in
> preinstall it wipes out both pipestat registers and again in
> postinstall, clearing status bits this time. That means that
> vblank_enabled is 1 and pipestat is empty. As long as there is a
> consumer asking for vblank, vblank_disable_fn never fires to clean
> all of this mess up. vblank_get won't ever actually turn vblanks
> back on, because it thinks they are already on. So the client just
> hangs there.
>
> I think that all of the libdrm code to deal with clients stalling on
> vblank was probably not needed. What happens now, is that while you
> are switched away or in dpms sleep, the client requesting vblank just
> repeatedly fires the timeout, rather than just stalling until you come
> back and seeing that the vblank counter has jumped way ahead of it and
> going on. As it is now, it continues to render one frame / sec while
> it is offscreen.
Yeah that does look like a real problem... Can we check whether the
handler has been installed at modeset time instead though? E.g.
(totally untested):
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 93e677a..f2e4e1c 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -504,7 +504,7 @@ int drm_modeset_ctl(struct drm_device *dev, void
*data, int crtc, ret = 0;
/* If drm_vblank_init() hasn't been called yet, just no-op */
- if (!dev->num_crtcs)
+ if (!dev->num_crtcs || !dev->irq_enabled)
goto out;
crtc = modeset->crtc;
Unfortunately, the rules keep changing here. When we first pushed this
stuff we were assuming that interrupts & vblanks would be enabled at
load time and stay on forever. But now we have vblank init at load
time, but interrupts going on & off at VT switch and startup time... it
really messes up the logic.
--
Jesse Barnes, Intel Open Source Technology Center
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