[PATCH] drm/i915: Check that the plane points to the pipe's framebuffer before enabling

[Chris Wilson <chris@chris-wilson.co.uk>]

Knut Petersen reported a GPU hang when he left x11perf running
overnight. The error state quite clearly indicates that plane A was
enabled without being fully setup:

PGTBL_ER: 0x00000010
    Display A: Invalid GTT PTE
Plane [0]:
  CNTR: c1000000
  STRIDE: 00000c80
  SIZE: 03ff04ff
  POS: 00000000
  ADDR: 00000000

[GTT offset on his system being pinned for the ringbuffer.]

This is a simple debugging patch to assert that this cannot be so!

References: https://bugs.freedesktop.org/show_bug.cgi?id=36246
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
---
 drivers/gpu/drm/i915/intel_display.c |   25 +++++++++++++++++++++++++
 1 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 7734d1e..82c22a3 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1274,6 +1274,30 @@ static void intel_disable_pipe(struct drm_i915_private *dev_priv,
 	intel_wait_for_pipe_off(dev_priv->dev, pipe);
 }
 
+/* Check that the DSPADDR points to the right framebufffer for the pipe. */
+static void assert_fb_bound_to_plane(struct drm_i915_private *dev_priv,
+				     enum pipe pipe, enum plane *plane)
+{
+	struct drm_crtc *crtc;
+	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
+	u32 val, base, size;
+
+	crtc = intel_get_crtc_for_pipe(dev, pipe);
+	if (WARN(crtc->fb == NULL,
+		 "no framebuffer attached to pipe %c\n",
+		 pipe_name(pipe)))
+		return;
+
+	intel_fb = to_intel_framebuffer(crtc->fb);
+	base = intel_fb->obj->gtt_offset;
+	size = intel_fb->obj->base.size;
+
+	val = I915_READ(DSPADDR(plane));
+	WARN(val < offset || val >= base + size,
+	     "mismatching framebuffer for plane %c attached to pipe %c\n",
+	     plane_name(plane), pipe_name(pipe));
+}
+
 /**
  * intel_enable_plane - enable a display plane on a given pipe
  * @dev_priv: i915 private structure
@@ -1290,6 +1314,7 @@ static void intel_enable_plane(struct drm_i915_private *dev_priv,
 
 	/* If the pipe isn't enabled, we can't pump pixels and may hang */
 	assert_pipe_enabled(dev_priv, pipe);
+	assert_fb_bound_to_plane(dev_priv, pipe, plane);
 
 	reg = DSPCNTR(plane);
 	val = I915_READ(reg);
-- 
1.7.4.1