Double buffering for i.MX53 fb driver (fix #721)

Enable optinal support for double buffering in the i.MX53 framebuffer
driver. This prevents flickering in certain scenarios, where applications
directly render in the framebuffer dataspace given by the driver.

os/src/drivers/framebuffer/imx53/driver.h

@@ -87,8 +87,6 @@ class Framebuffer::Driver
 			return true;
 		}
 
-		Mode   mode() { return Mode(_width, _height, Mode::RGB565); }
-		size_t size() { return BYTES_PER_PIXEL * _width * _height;  }
-
-		Ipu &ipu() { return _ipu; }
+		Mode mode() { return Mode(_width, _height, Mode::RGB565); }
+		Ipu &ipu()  { return _ipu; }
 };

os/src/drivers/framebuffer/imx53/main.cc

@@ -1,6 +1,7 @@
 /*
  * \brief  Frame-buffer driver for the i.MX53
  * \author Nikolay Golikov <nik@ksyslabs.org>
+ * \author Stefan Kalkowski <stefan.kalkowski@genode-labs.com>
  * \date   2012-06-21
  */
 
@@ -11,6 +12,8 @@
 #include <base/printf.h>
 #include <base/sleep.h>
 #include <os/static_root.h>
+#include <os/config.h>
+#include <blit/blit.h>
 
 /* local includes */
 #include <driver.h>
@@ -26,23 +29,34 @@ class Framebuffer::Session_component :
 {
 	private:
 
-		size_t               _size;
-		Dataspace_capability _ds;
-		addr_t               _phys_base;
-		Mode                 _mode;
+		bool     _buffered;
+		Mode     _mode;
+		size_t   _size;
+
+		/* dataspace uses a back buffer (if '_buffered' is true) */
+		Genode::Dataspace_capability _bb_ds;
+		void                        *_bb_addr;
+
+		/* dataspace of physical frame buffer */
+		Genode::Dataspace_capability _fb_ds;
+		void                        *_fb_addr;
 
 		Ipu &_ipu;
 
 	public:
 
-		Session_component(Driver &driver)
-		: _size(driver.size()),
-		  _ds(env()->ram_session()->alloc(_size, false)),
-		  _phys_base(Dataspace_client(_ds).phys_addr()),
+		Session_component(Driver &driver, bool buffered)
+		: _buffered(buffered),
 		  _mode(driver.mode()),
+		  _size(_mode.bytes_per_pixel() * _mode.width() * _mode.height()),
+		  _bb_ds(buffered ? Genode::env()->ram_session()->alloc(_size)
+		                  : Genode::Ram_dataspace_capability()),
+		  _bb_addr(buffered ? (void*)Genode::env()->rm_session()->attach(_bb_ds) : 0),
+		  _fb_ds(Genode::env()->ram_session()->alloc(_size, false)),
+		  _fb_addr((void*)Genode::env()->rm_session()->attach(_fb_ds)),
 		  _ipu(driver.ipu())
 		{
-			if (!driver.init(_phys_base)) {
+			if (!driver.init(Dataspace_client(_fb_ds).phys_addr())) {
 				PERR("Could not initialize display");
 				struct Could_not_initialize_display : Exception { };
 				throw Could_not_initialize_display();
@@ -54,16 +68,48 @@ class Framebuffer::Session_component :
 		 **  Framebuffer::session interface  **
 		 **************************************/
 
-		Dataspace_capability dataspace()                  { return _ds;   }
-		void release()                                    { }
-		Mode mode() const                                 { return _mode; }
+		Dataspace_capability dataspace() { return _buffered ? _bb_ds : _fb_ds; }
+		void release()                   { }
+		Mode mode() const                { return _mode; }
 		void mode_sigh(Genode::Signal_context_capability) { }
-		void refresh(int, int, int, int)                  { }
+
+		void refresh(int x, int y, int w, int h)
+		{
+			if (!_buffered) return;
+
+			/* clip specified coordinates against screen boundaries */
+			int x2 = min(x + w - 1, (int)_mode.width()  - 1),
+				y2 = min(y + h - 1, (int)_mode.height() - 1);
+			int x1 = max(x, 0),
+				y1 = max(y, 0);
+			if (x1 > x2 || y1 > y2) return;
+
+			int bypp = _mode.bytes_per_pixel();
+
+			/* copy pixels from back buffer to physical frame buffer */
+			char *src = (char *)_bb_addr + bypp*(_mode.width()*y + x),
+			     *dst = (char *)_fb_addr + bypp*(_mode.width()*y + x);
+
+			blit(src, bypp*_mode.width(), dst, bypp*_mode.width(),
+				 bypp*(x2 - x1 + 1), y2 - y1 + 1);
+		}
 
 		void overlay(Genode::addr_t phys_base, int x, int y, int alpha) {
 			_ipu.overlay(phys_base, x, y, alpha); }
 };
 
+
+static bool config_attribute(const char *attr_name)
+{
+	bool result = false;
+	try {
+		result =
+			Genode::config()->xml_node().attribute(attr_name).has_value("yes"); }
+	catch (...) {}
+	return result;
+}
+
+
 int main(int, char **)
 {
 	Genode::printf("Starting i.MX53 framebuffer driver\n");
@@ -76,7 +122,7 @@ int main(int, char **)
 	static Cap_connection cap;
 	static Rpc_entrypoint ep(&cap, STACK_SIZE, "fb_ep");
 
-	static Session_component                 fb_session(driver);
+	static Session_component fb_session(driver, config_attribute("buffered"));
 	static Static_root<Framebuffer::Session> fb_root(ep.manage(&fb_session));
 
 	env()->parent()->announce(ep.manage(&fb_root));

os/src/drivers/framebuffer/imx53/target.mk

@@ -1,7 +1,7 @@
 TARGET   = fb_drv
 REQUIRES = imx53
 SRC_CC   = main.cc
-LIBS     = base
+LIBS     = base blit
 INC_DIR += $(PRG_DIR)
 
 vpath main.cc $(PRG_DIR)