[PATCH 3.13 125/212] drm/i915: Increase WM memory latency values on SNB

[Kamal Mostafa]

3.13.11.4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala at linux.intel.com>

commit e95a2f7509f5219177d6821a0a8754f93892ca56 upstream.

On SNB the BIOS provided WM memory latency values seem insufficient to
handle high resolution displays.

In this particular case the display mode was a 2560x1440 at 60Hz, which
makes the pixel clock 241.5 MHz. It was empirically found that a memory
latency value if 1.2 usec is enough to avoid underruns, whereas the BIOS
provided value of 0.7 usec was clearly too low. Incidentally 1.2 usec
is what the typical BIOS provided values are on IVB systems.

Increase the WM memory latency values to at least 1.2 usec on SNB.
Hopefully this won't have a significant effect on power consumption.

v2: Increase the latency values regardless of the pixel clock

Cc: Robert N <crshman at gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70254
Tested-by: Robert Navarro <crshman at gmail.com>
Tested-by: Vitaly Minko <vitaly.minko at gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index e2d10ce..4128d0e 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2563,6 +2563,43 @@ static void intel_print_wm_latency(struct drm_device *dev,
 	}
 }
 
+static bool ilk_increase_wm_latency(struct drm_i915_private *dev_priv,
+				    uint16_t wm[5], uint16_t min)
+{
+	int level, max_level = ilk_wm_max_level(dev_priv->dev);
+
+	if (wm[0] >= min)
+		return false;
+
+	wm[0] = max(wm[0], min);
+	for (level = 1; level <= max_level; level++)
+		wm[level] = max_t(uint16_t, wm[level], DIV_ROUND_UP(min, 5));
+
+	return true;
+}
+
+static void snb_wm_latency_quirk(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	bool changed;
+
+	/*
+	 * The BIOS provided WM memory latency values are often
+	 * inadequate for high resolution displays. Adjust them.
+	 */
+	changed = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 12) |
+		ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_latency, 12) |
+		ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_latency, 12);
+
+	if (!changed)
+		return;
+
+	DRM_DEBUG_KMS("WM latency values increased to avoid potential underruns\n");
+	intel_print_wm_latency(dev, "Primary", dev_priv->wm.pri_latency);
+	intel_print_wm_latency(dev, "Sprite", dev_priv->wm.spr_latency);
+	intel_print_wm_latency(dev, "Cursor", dev_priv->wm.cur_latency);
+}
+
 static void intel_setup_wm_latency(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -2580,6 +2617,9 @@ static void intel_setup_wm_latency(struct drm_device *dev)
 	intel_print_wm_latency(dev, "Primary", dev_priv->wm.pri_latency);
 	intel_print_wm_latency(dev, "Sprite", dev_priv->wm.spr_latency);
 	intel_print_wm_latency(dev, "Cursor", dev_priv->wm.cur_latency);
+
+	if (IS_GEN6(dev))
+		snb_wm_latency_quirk(dev);
 }
 
 static void hsw_compute_wm_parameters(struct drm_crtc *crtc,
-- 
1.9.1