[Intel-gfx] [PATCH] drm/i915: Only write watermark registers if a pipe is active

[Matt Roper]

If all pipes are off, then we may have entered runtime suspend and
writing these registers will have no effect anyway.  When a pipe is
re-enabled, it's crtc_enable will take care of programming appropriate
watermark values.

Cc: arun.siluvery at linux.intel.com
Cc: ville.syrjala at linux.intel.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94349
Fixes: ed4a6a7ca853 ("drm/i915: Add two-stage ILK-style watermark programming (v11)")
Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
---
I've still been unable to reproduce this defect on my SNB system; none of the
suggested tests people have noted in Bugzilla have triggered it for me.  But
based on the stack trace I'm guessing that the problem happens because we've
disabled the last pipe and gone into runtime suspend before we get around to
optimizing the watermarks.

I'm not super familiar with the details of runtime PM, so if there's a better
way this should be handled, I'm open to suggestions.

 drivers/gpu/drm/i915/intel_pm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index f65e841..8c7fddf 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2802,8 +2802,6 @@ static void ilk_write_wm_values(struct drm_i915_private *dev_priv,
 		I915_WRITE(WM2_LP_ILK, results->wm_lp[1]);
 	if (dirty & WM_DIRTY_LP(3) && previous->wm_lp[2] != results->wm_lp[2])
 		I915_WRITE(WM3_LP_ILK, results->wm_lp[2]);
-
-	dev_priv->wm.hw = *results;
 }
 
 bool ilk_disable_lp_wm(struct drm_device *dev)
@@ -3731,7 +3729,10 @@ static void ilk_program_watermarks(struct drm_i915_private *dev_priv)
 
 	ilk_compute_wm_results(dev, best_lp_wm, partitioning, &results);
 
-	ilk_write_wm_values(dev_priv, &results);
+	if (config.num_pipes_active > 0)
+		ilk_write_wm_values(dev_priv, &results);
+
+	dev_priv->wm.hw = results;
 }
 
 static void ilk_initial_watermarks(struct intel_crtc_state *cstate)
-- 
2.1.4