[Intel-gfx] [PATCH] i915: add page flipping ioctl

[Chris Wilson]

On Mon, 2009-02-16 at 10:55 -0800, Jesse Barnes wrote:
> On Sunday, February 15, 2009 4:02 pm Chris Wilson wrote:
> > On my i915, the flip never occurs and we wait forever on the the vblank.
> > So I presume the command we sent the chip is invalid, or we miss the
> > irq? (I double-checked with lockdep in case I had missed an obvious
> > dead-lock.) Comments on the patch itself inline.
> 
> Thanks a lot for looking at this and testing.
> 
> Hm, maybe you're not getting vblank interrupts at all?  Do you see the count 
> increasing?  Is the IRQ registered?

Apparently, the vblank is never being enabled... Adding a BUG_ON() to
drm_vblank_put() soon identified the unbalanced culprit. So it appears
that drm_vblank_pre_modeset() can fail to enable vblank, obviously
because at that point we have never enabled vblank in pipeconf - but we
unconditionally decrement the vblank reference counter afterwards. Ok,
so now I see lots of vblank interrupts but the display is still snafu.

The following patch is a crude fix.

>From 1c4fa54654a604e0ea604553b983dca737a76e99 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris at chris-wilson.co.uk>
Date: Thu, 19 Feb 2009 14:48:22 +0000
Subject: [PATCH] drm: Correct unbalanced drm_vblank_put() during mode
setting.

The first time we install a mode, the vblank will be disabled for a pipe
and so drm_vblank_get() in drm_vblank_pre_modeset() will fail. As we
unconditionally call drm_vblank_put() afterwards, the vblank reference
counter becomes unbalanced.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_irq.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 3795dbc..93e677a 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -435,6 +435,8 @@ EXPORT_SYMBOL(drm_vblank_get);
  */
 void drm_vblank_put(struct drm_device *dev, int crtc)
 {
+	BUG_ON (atomic_read (&dev->vblank_refcount[crtc]) == 0);
+
 	/* Last user schedules interrupt disable */
 	if (atomic_dec_and_test(&dev->vblank_refcount[crtc]))
 		mod_timer(&dev->vblank_disable_timer, jiffies + 5*DRM_HZ);
@@ -460,8 +462,9 @@ void drm_vblank_pre_modeset(struct drm_device *dev,
int crtc)
 	 * so that interrupts remain enabled in the interim.
 	 */
 	if (!dev->vblank_inmodeset[crtc]) {
-		dev->vblank_inmodeset[crtc] = 1;
-		drm_vblank_get(dev, crtc);
+		dev->vblank_inmodeset[crtc] = 0x1;
+		if (drm_vblank_get(dev, crtc) == 0)
+			dev->vblank_inmodeset[crtc] |= 0x2;
 	}
 }
 EXPORT_SYMBOL(drm_vblank_pre_modeset);
@@ -473,9 +476,12 @@ void drm_vblank_post_modeset(struct drm_device
*dev, int crtc)
 	if (dev->vblank_inmodeset[crtc]) {
 		spin_lock_irqsave(&dev->vbl_lock, irqflags);
 		dev->vblank_disable_allowed = 1;
-		dev->vblank_inmodeset[crtc] = 0;
 		spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
-		drm_vblank_put(dev, crtc);
+
+		if (dev->vblank_inmodeset[crtc] & 0x2)
+			drm_vblank_put(dev, crtc);
+
+		dev->vblank_inmodeset[crtc] = 0;
 	}
 }
 EXPORT_SYMBOL(drm_vblank_post_modeset);
-- 
1.6.0.4