drm/i915: Organize Fence registers for future enablement.

Let's be optimistic that for future platforms this will remain the same
and reorg a bit.
This reorg in if blocks instead of switch make life easier for future
platform support addition.

v2: Jani pointed out I was missing reg_830 for some gen3 platforms. So let's make
    this platforms subcases of Gen checks.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -3277,17 +3277,12 @@ static void i915_gem_write_fence(struct drm_device *dev, int reg,
 	     "bogus fence setup with stride: 0x%x, tiling mode: %i\n",
 	     obj->stride, obj->tiling_mode);
 
-	switch (INTEL_INFO(dev)->gen) {
-	case 9:
-	case 8:
-	case 7:
-	case 6:
-	case 5:
-	case 4: i965_write_fence_reg(dev, reg, obj); break;
-	case 3: i915_write_fence_reg(dev, reg, obj); break;
-	case 2: i830_write_fence_reg(dev, reg, obj); break;
-	default: BUG();
-	}
+	if (IS_GEN2(dev))
+		i830_write_fence_reg(dev, reg, obj);
+	else if (IS_GEN3(dev))
+		i915_write_fence_reg(dev, reg, obj);
+	else if (INTEL_INFO(dev)->gen >= 4)
+		i965_write_fence_reg(dev, reg, obj);
 
 	/* And similarly be paranoid that no direct access to this region
 	 * is reordered to before the fence is installed.

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -764,32 +764,21 @@ static void i915_gem_record_fences(struct drm_device *dev,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	int i;
 
-	/* Fences */
-	switch (INTEL_INFO(dev)->gen) {
-	case 9:
-	case 8:
-	case 7:
-	case 6:
-		for (i = 0; i < dev_priv->num_fence_regs; i++)
-			error->fence[i] = I915_READ64(FENCE_REG_SANDYBRIDGE_0 + (i * 8));
-		break;
-	case 5:
-	case 4:
-		for (i = 0; i < 16; i++)
-			error->fence[i] = I915_READ64(FENCE_REG_965_0 + (i * 8));
-		break;
-	case 3:
-		if (IS_I945G(dev) || IS_I945GM(dev) || IS_G33(dev))
-			for (i = 0; i < 8; i++)
-				error->fence[i+8] = I915_READ(FENCE_REG_945_8 + (i * 4));
-	case 2:
+	if (IS_GEN3(dev) || IS_GEN2(dev)) {
 		for (i = 0; i < 8; i++)
 			error->fence[i] = I915_READ(FENCE_REG_830_0 + (i * 4));
-		break;
-
-	default:
-		BUG();
-	}
+		if (IS_I945G(dev) || IS_I945GM(dev) || IS_G33(dev))
+			for (i = 0; i < 8; i++)
+				error->fence[i+8] = I915_READ(FENCE_REG_945_8 +
+							      (i * 4));
+	} else if (IS_GEN5(dev) || IS_GEN4(dev))
+		for (i = 0; i < 16; i++)
+			error->fence[i] = I915_READ64(FENCE_REG_965_0 +
+						      (i * 8));
+	else if (INTEL_INFO(dev)->gen >= 6)
+		for (i = 0; i < dev_priv->num_fence_regs; i++)
+			error->fence[i] = I915_READ64(FENCE_REG_SANDYBRIDGE_0 +
+						      (i * 8));
 }