drm/i915: IVB/HSW have 32 fence register

Increase the number of fence registers to 32 on IVB/HSW. VLV however
only has 16 fence registers according to the docs.

Increasing the number of fences was attempted before [1], but there was
some uncertainty about the maximum CPU fence number for FBC. Since then
BSpec has been updated to state that there are in fact 32 fence registers,
and the CPU fence number field in the SNB_DPFC_CTL_SA register is 5 bits,
and the CPU fence number field in the ILK_DPFC_CONTROL register must be
zero. So now it all makes sense.

[1] http://lists.freedesktop.org/archives/intel-gfx/2011-October/012865.html

v2: Include some background information based on the previous attempt
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -195,9 +195,9 @@ struct drm_i915_master_private {
 	struct _drm_i915_sarea *sarea_priv;
 };
 #define I915_FENCE_REG_NONE -1
-#define I915_MAX_NUM_FENCES 16
-/* 16 fences + sign bit for FENCE_REG_NONE */
-#define I915_MAX_NUM_FENCE_BITS 5
+#define I915_MAX_NUM_FENCES 32
+/* 32 fences + sign bit for FENCE_REG_NONE */
+#define I915_MAX_NUM_FENCE_BITS 6
 
 struct drm_i915_fence_reg {
 	struct list_head lru_list;

drivers/gpu/drm/i915/i915_gem.c

@@ -4190,7 +4190,9 @@ i915_gem_load(struct drm_device *dev)
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		dev_priv->fence_reg_start = 3;
 
-	if (INTEL_INFO(dev)->gen >= 4 || IS_I945G(dev) || IS_I945GM(dev) || IS_G33(dev))
+	if (INTEL_INFO(dev)->gen >= 7 && !IS_VALLEYVIEW(dev))
+		dev_priv->num_fence_regs = 32;
+	else if (INTEL_INFO(dev)->gen >= 4 || IS_I945G(dev) || IS_I945GM(dev) || IS_G33(dev))
 		dev_priv->num_fence_regs = 16;
 	else
 		dev_priv->num_fence_regs = 8;

drivers/gpu/drm/i915/i915_irq.c

@@ -1213,7 +1213,7 @@ static void i915_gem_record_fences(struct drm_device *dev,
 	switch (INTEL_INFO(dev)->gen) {
 	case 7:
 	case 6:
-		for (i = 0; i < 16; i++)
+		for (i = 0; i < dev_priv->num_fence_regs; i++)
 			error->fence[i] = I915_READ64(FENCE_REG_SANDYBRIDGE_0 + (i * 8));
 		break;
 	case 5: