libpayload: cbgfx: Support buffered I/O

For payloads with UI based on CBGFX, they usually start by calling
clear_canvas or clear_screen and then draw the UI elements. However,
that makes the screen flicker.

A typical solution is to identify and minimize the area to redraw.
However for payloads with complicated UI and do not care about latency,
an alternative is to enable buffered I/O.

The new enable_graphics_buffer() will redirect all graphics I/O
into an invisible working buffer. To flush (redraw) the buffer to the
real screen, call flush_graphics_buffer(). To stop buffering, call
disable_graphics_buffer().

BUG=None
TEST=Add the enable, flush and disable calls to payload 'depthcharge',
     built a firmware and boots into Chrome OS recover UI. No more
     flickering. The average rendering time on x86 platform is 1.2ms.

Change-Id: Id60a2824fd9e164feae16b92b68b003beabea8d3
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44654
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/payloads/libpayload/include/cbgfx.h b/payloads/libpayload/include/cbgfx.h
index 85b61a7b10..72e512267a 100644
--- a/payloads/libpayload/include/cbgfx.h
+++ b/payloads/libpayload/include/cbgfx.h
@@ -56,6 +56,8 @@
 #define CBGFX_ERROR_FRAMEBUFFER_ADDR	0x15
 /* portrait screen not supported */
 #define CBGFX_ERROR_PORTRAIT_SCREEN	0x16
+/* cannot use buffered I/O */
+#define CBGFX_ERROR_GRAPHICS_BUFFER	0x17
 
 struct fraction {
 	int32_t n;
@@ -272,3 +274,24 @@ void clear_blend(void);
  *	0   = min alpha argument, 0% opacity
  */
 #define ALPHA(percentage) MIN(255, (256 * percentage / 100))
+
+/**
+ * Enable buffered I/O. All CBGFX operations will be redirected to a working
+ * buffer, and only updated (redrawn) when flush_graphics_buffer() is called.
+ *
+ * @return CBGFX_* error codes
+ */
+int enable_graphics_buffer(void);
+
+/**
+ * Redraw buffered graphics data to real screen if graphics buffer is already
+ * enabled.
+ *
+ * @return CBGFX_* error codes
+ */
+int flush_graphics_buffer(void);
+
+/**
+ * Stop using buffered I/O and release allocated memory.
+ */
+void disable_graphics_buffer(void);