On Apr 28, 2011, at 9:47 AM, Christopher James Halse Rogers wrote:
On Wed, 2011-04-27 at 17:50 +0200, Mario Kleiner wrote:
On Apr 27, 2011, at 10:58 AM, dri-devel-request@xxxxxxxxxxxxxxxxxxxxx
wrote:
Message: 5
Date: Wed, 27 Apr 2011 10:38:14 +0200
From: Michel D?nzer <michel@xxxxxxxxxxx>
Subject: Re: [PATCH 2/3] drm: Warn if vblank state has become
inconsistent.
To: christopher.halse.rogers@xxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Message-ID: <1303893494.5633.129.camel@xxxxxxxxxx>
Content-Type: text/plain; charset="UTF-8"
On Mit, 2011-04-27 at 16:10 +1000,
christopher.halse.rogers@xxxxxxxxxxxxx wrote:
From: Christopher James Halse Rogers
<christopher.halse.rogers@xxxxxxxxxxxxx>
After emitting all the waiting vblank events no-one should hold
a vblank reference. Emit a warning if this is not the case.
Signed-off-by: Christopher James Halse Rogers
<christopher.halse.rogers@xxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_irq.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index a1f12cb..72407fa 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -960,6 +960,7 @@ void drm_vblank_off(struct drm_device *dev,
int crtc)
e->event.sequence);
}
+ WARN_ON(atomic_read(&dev->vblank_refcount[crtc]) != 0);
spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
}
EXPORT_SYMBOL(drm_vblank_off);
Reviewed-by: Michel D?nzer <michel@xxxxxxxxxxx>
Any pending kms pageflip will also hold a reference on the vblank of
a crtc, so having the refcount non-zero there is not really a sign of
inconsistency, so i'm not sure if a warning is appropriate there.
But at this point the vblank interrupts have been disabled, or at
least
the driver's disable function has been called. Will that not mean
that
any pending pageflips will wait indefinitely for a vblank interrupt
that's not going to come - ie: exactly the state we're warning
against?
Ok, if that is the state we're warning against, then the warning
makes sense. But it would make more sense to somehow handle this more
gracefully. The pageflip completion path does depend on vblank irq's
to unpin buffers, release fences and notify user apps of swap
completion. Hanging there due to disabled vblank irq sounds bad.
Otoh the only caller of drm_vblank_off() i can find in 2.6.38 is the
crtc disable code in intel_display.c and those routines protect
against pending pageflips - they wait for all pageflips to finish
before calling drm_vblank_off().
If this warning is just a precaution against possible future bugs
then i happily rest my case.
-mario
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