[PATCH 02/11] drm/i915: Introduce FBC DocBook.

[Paulo Zanoni <przanoni@gmail.com>]

From: Rodrigo Vivi <rodrigo.vivi@intel.com>

No functional changes.

v2 (Paulo): Rebase.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
 Documentation/DocBook/drm.tmpl   |  5 ++++
 drivers/gpu/drm/i915/intel_fbc.c | 57 ++++++++++++++++++++++++++++++++++------
 2 files changed, 54 insertions(+), 8 deletions(-)

diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index 85287cb..8b780ab 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -3926,6 +3926,11 @@ int num_ioctls;</synopsis>
 !Idrivers/gpu/drm/i915/intel_psr.c
       </sect2>
       <sect2>
+	<title>Frame Buffer Compression (FBC)</title>
+!Pdrivers/gpu/drm/i915/intel_fbc.c Frame Buffer Compression (FBC)
+!Idrivers/gpu/drm/i915/intel_fbc.c
+      </sect2>
+      <sect2>
         <title>DPIO</title>
 !Pdrivers/gpu/drm/i915/i915_reg.h DPIO
 	<table id="dpiox2">
diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index f1eeb86..7686573 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -21,20 +21,31 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
-#include "intel_drv.h"
-#include "i915_drv.h"
-
-/* FBC, or Frame Buffer Compression, is a technique employed to compress the
- * framebuffer contents in-memory, aiming at reducing the required bandwidth
+/**
+ * DOC: Frame Buffer Compression (FBC)
+ *
+ * FBC is a technique employed to compress the framebuffer contents
+ * in-memory, aiming at reducing the required bandwidth
  * during in-memory transfers and, therefore, reduce the power packet.
  *
+ * FBC is primarily a memory power savings technology. That is the major
+ * benefit is to the memory power while displaying the processor graphics
+ * information to the display. FBC works by compressing the amount of memory
+ * used by the display. It means that it is total transparent to user space.
+ *
  * The benefits of FBC are mostly visible with solid backgrounds and
- * variation-less patterns.
+ * variation-less patterns. It comes from keeping the memory footprint small
+ * and having fewer memory pages opened and accessed for refreshing the display.
  *
- * FBC-related functionality can be enabled by the means of the
- * i915.i915_fbc_enable parameter
+ * i915 is responsible to reserve stolen memory for FBC and configure its
+ * offset on proper register. The hardware takes care of all
+ * compress/decompress. However there are many known cases where we have to
+ * forcibly disable it to allow proper screen updates.
  */
 
+#include "intel_drv.h"
+#include "i915_drv.h"
+
 static void i8xx_fbc_disable(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -318,6 +329,12 @@ static void gen7_fbc_enable(struct drm_crtc *crtc)
 	DRM_DEBUG_KMS("enabled fbc on plane %c\n", plane_name(intel_crtc->plane));
 }
 
+/**
+ * intel_fbc_enabled - Is FBC enabled?
+ * @dev: the drm_device
+ *
+ * This function is used to verify the current state of FBC.
+ */
 bool intel_fbc_enabled(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -325,6 +342,18 @@ bool intel_fbc_enabled(struct drm_device *dev)
 	return dev_priv->fbc.enabled;
 }
 
+/**
+ * bdw_fbc_sw_flush - FBC Software Flush for Broadwell.
+ * @dev: the drm_device
+ * @value: Value to be set on MSG_FBC_REND_STATE. Possible values are
+ *         FBC_REND_NUKE and FBC_REND_CACHE_CLEAN.
+ *
+ * This function is needed on Broadwell to perform Nuke or Cache clean on
+ * software side over MMIO.
+ * On Broadwell, due a hardware bug, MSG_FBC_REND_STATE stay in a forbidden
+ * address that has a huge risk of causing GPU Hangs if set with LRI on some
+ * command streamers.
+ */
 void bdw_fbc_sw_flush(struct drm_device *dev, u32 value)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -429,6 +458,12 @@ static void intel_fbc_enable(struct drm_crtc *crtc)
 	schedule_delayed_work(&work->work, msecs_to_jiffies(50));
 }
 
+/**
+ * intel_fbc_disable - disable FBC
+ * @dev: the drm_device
+ *
+ * This function disables FBC.
+ */
 void intel_fbc_disable(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -643,6 +678,12 @@ out_disable:
 	i915_gem_stolen_cleanup_compression(dev);
 }
 
+/**
+ * intel_fbc_init - Initialize FBC
+ * @dev_priv: the i915 device
+ *
+ * This function might be called during PM init process.
+ */
 void intel_fbc_init(struct drm_i915_private *dev_priv)
 {
 	if (!HAS_FBC(dev_priv)) {
-- 
2.1.3

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