Re: [PATCH 1/3] drm/i915/skl+: Don't trust cached ddb values

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Hi Maarten,

Thanks for review :)


On Tuesday 30 May 2017 03:30 PM, Maarten Lankhorst wrote:
Op 26-05-17 om 17:15 schreef Mahesh Kumar:
Don't trust cached DDB values. Recalculate the ddb value if cached value
is zero.

If i915 is build as a module, there may be a race condition when
cursor_disable call comes even before intel_fbdev_initial_config.
Which may lead to cached value being 0. And further commit will fail
until a modeset.

Signed-off-by: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
---
  drivers/gpu/drm/i915/intel_pm.c | 15 ++++++++++-----
  1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 936eef1634c7..b67be1355e39 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3721,6 +3721,7 @@ skl_ddb_get_pipe_allocation_limits(struct drm_device *dev,
  	struct drm_i915_private *dev_priv = to_i915(dev);
  	struct drm_crtc *for_crtc = cstate->base.crtc;
  	unsigned int pipe_size, ddb_size;
+	unsigned int active_crtcs;
  	int nth_active_pipe;
if (WARN_ON(!state) || !cstate->base.active) {
@@ -3731,10 +3732,11 @@ skl_ddb_get_pipe_allocation_limits(struct drm_device *dev,
  	}
if (intel_state->active_pipe_changes)
-		*num_active = hweight32(intel_state->active_crtcs);
+		active_crtcs = intel_state->active_crtcs;
  	else
-		*num_active = hweight32(dev_priv->active_crtcs);
+		active_crtcs = dev_priv->active_crtcs;
+ *num_active = hweight32(active_crtcs);
  	ddb_size = INTEL_INFO(dev_priv)->ddb_size;
  	WARN_ON(ddb_size == 0);
@@ -3754,12 +3756,15 @@ skl_ddb_get_pipe_allocation_limits(struct drm_device *dev,
  		 * copy from old state to be sure
  		 */
  		*alloc = to_intel_crtc_state(for_crtc->state)->wm.skl.ddb;
-		return;
+		if (!skl_ddb_entry_size(alloc))
+			DRM_DEBUG_KMS("Cached pipe DDB is 0 recalculate\n");
+		else
+			return;
  	}
- nth_active_pipe = hweight32(intel_state->active_crtcs &
+	nth_active_pipe = hweight32(active_crtcs &
  				    (drm_crtc_mask(for_crtc) - 1));
-	pipe_size = ddb_size / hweight32(intel_state->active_crtcs);
+	pipe_size = ddb_size / hweight32(active_crtcs);
  	alloc->start = nth_active_pipe * ddb_size / *num_active;
  	alloc->end = alloc->start + pipe_size;
  }
I'd love it if you also add a warning somewhere for active pipe with no ddb allocation to prevent this from reoccuring in the future. :)
But with the root cause being a invalid ddb allocation at boot, won't the below one liner should fix it too, but better?
Above DEBUG message is actually warning. That will hit only if pipe is active & DDB allocated for that pipe is "0" (we do return from caller if !cstate->active). I can reword the msg to be WARN & make it something like "Pipe is active with No DDB allocated, recompute ddb now". This will fix the issue as well as add warning msg.


I'l ltest it when f3-kbl becomes available again.

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index a488e068c3d6..63a47909f618 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5051,7 +5051,7 @@ skl_compute_wm(struct drm_atomic_state *state)
  	 */
  	for_each_new_crtc_in_state(state, crtc, cstate, i)
  		changed = true;
-	if (!changed)
+	if (!changed && !to_i915(state->dev)->wm.distrust_bios_wm)
  		return 0;
This change should also solve the issue during boot.

-Mahesh
  	/* Clear all dirty flags */


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