Patch "drm/i915: Always recompute watermarks when distrust_bios_wm is set, v2." has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    drm/i915: Always recompute watermarks when distrust_bios_wm is set, v2.

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-i915-always-recompute-watermarks-when-distrust_bios_wm-is-set-v2.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 4e3aed844547f63614363a386de126e6304e55fb Mon Sep 17 00:00:00 2001
From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Date: Wed, 31 May 2017 17:42:36 +0200
Subject: drm/i915: Always recompute watermarks when distrust_bios_wm is set, v2.

From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

commit 4e3aed844547f63614363a386de126e6304e55fb upstream.

On some systems there can be a race condition in which no crtc state is
added to the first atomic commit. This results in all crtc's having a
null DDB allocation, causing a FIFO underrun on any update until the
first modeset.

Changes since v1:
- Do not take the connection_mutex, this is already done below.

Reported-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Inspired-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: 98d39494d375 ("drm/i915/gen9: Compute DDB allocation at atomic
check time (v4)")
Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170531154236.27180-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit 367d73d2806085bb507ab44c1f532640917fd5ca)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

---
 drivers/gpu/drm/i915/intel_pm.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4114,11 +4114,19 @@ skl_compute_wm(struct drm_atomic_state *
 	struct drm_crtc_state *cstate;
 	struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
 	struct skl_wm_values *results = &intel_state->wm_results;
+	struct drm_device *dev = state->dev;
 	struct skl_pipe_wm *pipe_wm;
 	bool changed = false;
 	int ret, i;
 
 	/*
+	 * When we distrust bios wm we always need to recompute to set the
+	 * expected DDB allocations for each CRTC.
+	 */
+	if (to_i915(dev)->wm.distrust_bios_wm)
+		changed = true;
+
+	/*
 	 * If this transaction isn't actually touching any CRTC's, don't
 	 * bother with watermark calculation.  Note that if we pass this
 	 * test, we're guaranteed to hold at least one CRTC state mutex,
@@ -4128,6 +4136,7 @@ skl_compute_wm(struct drm_atomic_state *
 	 */
 	for_each_crtc_in_state(state, crtc, cstate, i)
 		changed = true;
+
 	if (!changed)
 		return 0;
 


Patches currently in stable-queue which might be from maarten.lankhorst@linux.intel.com are

queue-4.9/drm-i915-always-recompute-watermarks-when-distrust_bios_wm-is-set-v2.patch
queue-4.9/drm-i915-check-for-null-i915_vma-in-intel_unpin_fb_obj.patch