From 0b5ab223e110f3a34b30e7b61e4ea68c03dba98b Mon Sep 17 00:00:00 2001
From: YiMing Tseng <yimingtseng@google.com>
Date: Thu, 11 Nov 2021 14:05:30 +0800
Subject: [PATCH] Add GRALLOC_FRAMEBUFFER_NUM configuration

Add config to set the NUM_BUFFERS. Set NUM_BUFFERS to 1 can
prevent page flipping and set it to a larger number can allow
userspace to fill up the following frame earlier.

Bug: 205917753
Change-Id: Ibf4a52a1e35f4a2404008a48b637cb82c4b46365
---
 modules/gralloc/Android.mk      | 3 +++
 modules/gralloc/framebuffer.cpp | 7 +++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/modules/gralloc/Android.mk b/modules/gralloc/Android.mk
index 439c95dd..4c4899ea 100644
--- a/modules/gralloc/Android.mk
+++ b/modules/gralloc/Android.mk
@@ -38,5 +38,8 @@ LOCAL_CFLAGS:= -DLOG_TAG=\"gralloc\" -Wno-missing-field-initializers
 ifeq ($(TARGET_USE_PAN_DISPLAY),true)
 LOCAL_CFLAGS += -DUSE_PAN_DISPLAY=1
 endif
+ifneq ($(GRALLOC_FRAMEBUFFER_NUM),)
+LOCAL_CFLAGS += -DNUM_BUFFERS=$(GRALLOC_FRAMEBUFFER_NUM)
+endif
 
 include $(BUILD_SHARED_LIBRARY)
diff --git a/modules/gralloc/framebuffer.cpp b/modules/gralloc/framebuffer.cpp
index b2ec3e44..fc220dbc 100644
--- a/modules/gralloc/framebuffer.cpp
+++ b/modules/gralloc/framebuffer.cpp
@@ -45,8 +45,10 @@
 #define USE_PAN_DISPLAY 0
 #endif
 
-// numbers of buffers for page flipping
+// Enabling page flipping by default
+#ifndef NUM_BUFFERS
 #define NUM_BUFFERS 2
+#endif
 
 
 enum {
@@ -157,7 +159,8 @@ int mapFrameBufferLocked(struct private_module_t* module, int format)
     info.activate = FB_ACTIVATE_NOW;
 
     /*
-     * Request NUM_BUFFERS screens (at lest 2 for page flipping)
+     * Request NUM_BUFFERS screens
+     * To enable page flipping, NUM_BUFFERS should be at least 2.
      */
     info.yres_virtual = info.yres * NUM_BUFFERS;