drm/i915/fbc: fix the check for already reserved fbc size

The check for previously reserved stolen space size for FBC in
i915_gem_stolen_setup_compression() did not take the compression
threshold into account. Fix this by storing and comparing to
uncompressed size instead.

The bug has been introduced in

commit 5e59f7175f96550ede91f58d267d2b551cb6fbba
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Mon Jun 30 10:41:24 2014 -0700

    drm/i915: Try harder to get FBC

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88975
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <benjamin.widawsky@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -772,7 +772,7 @@ struct intel_context {
 };
 
 struct i915_fbc {
-	unsigned long size;
+	unsigned long uncompressed_size;
 	unsigned threshold;
 	unsigned int fb_id;
 	enum plane plane;

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -231,7 +231,7 @@ static int i915_setup_compression(struct drm_device *dev, int size, int fb_cpp)
 			   dev_priv->mm.stolen_base + compressed_llb->start);
 	}
 
-	dev_priv->fbc.size = size / dev_priv->fbc.threshold;
+	dev_priv->fbc.uncompressed_size = size;
 
 	DRM_DEBUG_KMS("reserved %d bytes of contiguous stolen space for FBC\n",
 		      size);
@@ -253,7 +253,7 @@ int i915_gem_stolen_setup_compression(struct drm_device *dev, int size, int fb_c
 	if (!drm_mm_initialized(&dev_priv->mm.stolen))
 		return -ENODEV;
 
-	if (size < dev_priv->fbc.size)
+	if (size < dev_priv->fbc.uncompressed_size)
 		return 0;
 
 	/* Release any current block */
@@ -266,7 +266,7 @@ void i915_gem_stolen_cleanup_compression(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
-	if (dev_priv->fbc.size == 0)
+	if (dev_priv->fbc.uncompressed_size == 0)
 		return;
 
 	drm_mm_remove_node(&dev_priv->fbc.compressed_fb);
@@ -276,7 +276,7 @@ void i915_gem_stolen_cleanup_compression(struct drm_device *dev)
 		kfree(dev_priv->fbc.compressed_llb);
 	}
 
-	dev_priv->fbc.size = 0;
+	dev_priv->fbc.uncompressed_size = 0;
 }
 
 void i915_gem_cleanup_stolen(struct drm_device *dev)

drivers/gpu/drm/i915/intel_fbc.c

@@ -78,7 +78,8 @@ static void i8xx_fbc_enable(struct drm_crtc *crtc)
 
 	dev_priv->fbc.enabled = true;
 
-	cfb_pitch = dev_priv->fbc.size / FBC_LL_SIZE;
+	/* Note: fbc.threshold == 1 for i8xx */
+	cfb_pitch = dev_priv->fbc.uncompressed_size / FBC_LL_SIZE;
 	if (fb->pitches[0] < cfb_pitch)
 		cfb_pitch = fb->pitches[0];