[Intel-gfx] [PATCH] drm/i915: Only dump 'active' batch buffers

[Chris Wilson]

If we have a long sequence of batch buffers queued when running
intel_gpu_dump, then we will mysteriously fail to read back any of the
batches. This implements a work-around by only dumping the batch buffers
that are older than the current seqno, which are the ones most likely to
contain the error (and active HEAD pointer).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c |   29 ++++++++++++++++++++---------
 1 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index dd355ae..cc962e7 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -276,6 +276,12 @@ static void i915_dump_pages(struct seq_file *m, struct page **pages, int page_co
 	}
 }
 
+static int
+i915_seqno_passed(uint32_t seq1, uint32_t seq2)
+{
+	return (int32_t)(seq1 - seq2) >= 0;
+}
+
 static int i915_batchbuffer_info(struct seq_file *m, void *data)
 {
 	struct drm_info_node *node = (struct drm_info_node *) m->private;
@@ -283,21 +289,26 @@ static int i915_batchbuffer_info(struct seq_file *m, void *data)
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	struct drm_gem_object *obj;
 	struct drm_i915_gem_object *obj_priv;
-	int ret;
+	int ret = 0;
+	u32 seqno;
 
 	/* Avoid 'impossible' deadlock when debugging */
 	if (! spin_trylock(&dev_priv->mm.active_list_lock))
 		return -EBUSY;
 
+	/* Only show active batchbuffers to curtail the amount of data
+	 * returned (trying to return too many causes allocation failures,
+	 * and returning nothing).
+	 */
+	seqno = i915_get_gem_seqno(dev) + 2;
+
 	list_for_each_entry(obj_priv, &dev_priv->mm.active_list, list) {
 		obj = obj_priv->obj;
-		if (obj->read_domains & I915_GEM_DOMAIN_COMMAND) {
+		if (i915_seqno_passed(seqno, obj_priv->last_rendering_seqno) &&
+		    obj->read_domains & I915_GEM_DOMAIN_COMMAND) {
 		    ret = i915_gem_object_get_pages(obj);
-		    if (ret) {
-			    DRM_ERROR("Failed to get pages: %d\n", ret);
-			    spin_unlock(&dev_priv->mm.active_list_lock);
-			    return ret;
-		    }
+		    if (ret)
+			    goto out;
 
 		    seq_printf(m, "--- gtt_offset = 0x%08x\n", obj_priv->gtt_offset);
 		    i915_dump_pages(m, obj_priv->pages, obj->size / PAGE_SIZE);
@@ -306,9 +317,9 @@ static int i915_batchbuffer_info(struct seq_file *m, void *data)
 		}
 	}
 
+out:
 	spin_unlock(&dev_priv->mm.active_list_lock);
-
-	return 0;
+	return ret;
 }
 
 static int i915_ringbuffer_data(struct seq_file *m, void *data)
-- 
1.6.3.3