[Intel-gfx] [PATCH] drm/i915: initialize ring frequency scaling table on SNB

[Jesse Barnes]

The ring frequency scaling table tells the PCU to treat certain GPU
frequencies as if they were a given CPU frequency for purposes of
scaling the ring frequency.  Normally the PCU will scale the ring
frequency based on the CPU P-state, but with the table present, it will
also take the GPU frequency into account.  The scaling_factor used in
this patch may not be ideal, but is enough to increase performance in
nexuiz on a 1366x768 panel by about 20%.

The main downside of keeping the ring frequency high while the CPU is
at a low frequency (or asleep altogether) is increased power
consumption.  But then if you're keeping your GPU busy, you probably
want the extra performance.

Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 2f967af..15ee639 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3433,7 +3433,8 @@
 #define GEN6_PCODE_MAILBOX			0x138124
 #define   GEN6_PCODE_READY			(1<<31)
 #define   GEN6_READ_OC_PARAMS			0xc
-#define   GEN6_PCODE_WRITE_MIN_FREQ_TABLE	0x9
+#define   GEN6_PCODE_WRITE_MIN_FREQ_TABLE	0x8
 #define GEN6_PCODE_DATA				0x138128
+#define   GEN6_PCODE_FREQ_IA_RATIO_SHIFT	8
 
 #endif /* _I915_REG_H_ */
diff --git a/drivers/gpu/drm/i915/i915_suspend.c b/drivers/gpu/drm/i915/i915_suspend.c
index 60a94d2..03f0fac 100644
--- a/drivers/gpu/drm/i915/i915_suspend.c
+++ b/drivers/gpu/drm/i915/i915_suspend.c
@@ -870,8 +870,10 @@ int i915_restore_state(struct drm_device *dev)
 		intel_init_emon(dev);
 	}
 
-	if (IS_GEN6(dev))
+	if (IS_GEN6(dev)) {
 		gen6_enable_rps(dev_priv);
+		gen6_update_ring_freq(dev_priv);
+	}
 
 	/* Cache mode state */
 	I915_WRITE (CACHE_MODE_0, dev_priv->saveCACHE_MODE_0 | 0xffff0000);
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 86a3ec1..05c28eb 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7159,6 +7159,46 @@ void gen6_enable_rps(struct drm_i915_private *dev_priv)
 	mutex_unlock(&dev_priv->dev->struct_mutex);
 }
 
+void gen6_update_ring_freq(struct drm_i915_private *dev_priv)
+{
+	int min_freq = 15, max_freq = 32;
+	int gpu_freq, ia_freq;
+	int scaling_factor = 180;
+
+	mutex_lock(&dev_priv->dev->struct_mutex);
+	gen6_gt_force_wake_get(dev_priv);
+
+	/*
+	 * For each potential GPU frequency, load a ring frequency we'd like
+	 * to use for memory access.  We do this by specifying the IA frequency
+	 * the PCU should use as a reference to determine the ring frequency.
+	 */
+	for (gpu_freq = dev_priv->min_delay; gpu_freq <= dev_priv->max_delay;
+	     gpu_freq++) {
+		if (gpu_freq < min_freq) /* Use 800MHz min IA reference freq */
+			ia_freq = 800;
+		else if (gpu_freq > max_freq) /* Clamp to 3GHz IA ref. freq */
+			ia_freq = 3000;
+		else
+			ia_freq = (gpu_freq * scaling_factor) / 2;
+		ia_freq = DIV_ROUND_UP(ia_freq, 100);
+
+		I915_WRITE(GEN6_PCODE_DATA,
+			   (ia_freq << GEN6_PCODE_FREQ_IA_RATIO_SHIFT) |
+			   gpu_freq);
+		I915_WRITE(GEN6_PCODE_MAILBOX, GEN6_PCODE_READY |
+			   GEN6_PCODE_WRITE_MIN_FREQ_TABLE);
+		if (wait_for((I915_READ(GEN6_PCODE_MAILBOX) &
+			      GEN6_PCODE_READY) == 0, 10)) {
+			DRM_ERROR("pcode write of freq table timed out\n");
+			continue;
+		}
+	}
+
+	gen6_gt_force_wake_put(dev_priv);
+	mutex_unlock(&dev_priv->dev->struct_mutex);
+}
+
 static void ironlake_init_clock_gating(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -7777,8 +7817,10 @@ void intel_modeset_init(struct drm_device *dev)
 		intel_init_emon(dev);
 	}
 
-	if (IS_GEN6(dev))
+	if (IS_GEN6(dev)) {
 		gen6_enable_rps(dev_priv);
+		gen6_update_ring_freq(dev_priv);
+	}
 
 	INIT_WORK(&dev_priv->idle_work, intel_idle_update);
 	setup_timer(&dev_priv->idle_timer, intel_gpu_idle_timer,
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 9ffa61e..8ac3bd8 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -317,6 +317,7 @@ extern void intel_enable_clock_gating(struct drm_device *dev);
 extern void ironlake_enable_drps(struct drm_device *dev);
 extern void ironlake_disable_drps(struct drm_device *dev);
 extern void gen6_enable_rps(struct drm_i915_private *dev_priv);
+extern void gen6_update_ring_freq(struct drm_i915_private *dev_priv);
 extern void gen6_disable_rps(struct drm_device *dev);
 extern void intel_init_emon(struct drm_device *dev);