在Y:\LA.BR.1.2.4-05310-8x16.0\device\qcom\common\init\init_msm8916.c 中获取virtual_size值，根据不同的屏幕大小设置ro.sf.lcd_density。

其中PROP_LCDDENSITY的值在device/qcom/common/init/init_msm.h中定义：

#define VIRTUAL_SIZE "/sys/class/graphics/fb0/virtual_size"
#define BUF_SIZE 64void init_msm_properties(unsigned long msm_id, unsigned long msm_ver, char *board_type)
{char platform[PROP_VALUE_MAX];int rc;unsigned long virtual_size = 0;char str[BUF_SIZE];UNUSED(msm_id);UNUSED(msm_ver);rc = property_get("ro.board.platform", platform);if (!rc || !ISMATCH(platform, ANDROID_TARGET)){return;}rc = read_file2(VIRTUAL_SIZE, str, sizeof(str));if (rc) {virtual_size = strtoul(str, NULL, 0);}if(virtual_size >= 1080) {if (ISMATCH(board_type, "SBC")) {property_set(PROP_LCDDENSITY, "240");property_set(PROP_QEMU_NAVKEY, "0");} elseproperty_set(PROP_LCDDENSITY, "480");} else if (virtual_size >= 720) {// For 720x1280 resolutionproperty_set(PROP_LCDDENSITY, "320");} else if (virtual_size >= 480) {// For 480x854 resolution QRD.property_set(PROP_LCDDENSITY, "240");} elseproperty_set(PROP_LCDDENSITY, "320");if (msm_id >= 239 && msm_id <= 243) {property_set("media.msm8939hw", "1");}if (msm_id >= 268 && msm_id <= 271) {property_set("media.msm8929hw", "1");}if (msm_id == 206) {property_set("vidc.enc.narrow.searchrange", "0");}
}kernel/drivers/video/fbsysfs.cstatic ssize_t show_virtual(struct device *device,struct device_attribute *attr, char *buf)
{struct fb_info *fb_info = dev_get_drvdata(device);return snprintf(buf, PAGE_SIZE, "%d,%d\n", fb_info->var.xres_virtual,fb_info->var.yres_virtual);
}在Msm_fb.c (drivers\video\msm)  定义fb_info->var.xres_virtualvar->xres_virtual = panel_info->xres;
var->yres_virtual = panel_info->yres * mfd->fb_page +((PAGE_SIZE - remainder)/fix->line_length) * mfd->fb_page;

所以ro.sf.lcd_density最终是有分辨率决定的。

init_msm_properties函数被谁调用了呢？暂时没找到

为了更加便捷的修改ro.sf.lcd_density，后面做了一个实验：

1、  在android系统运行的时候通过adb 修改/system/build.prop文件，添加一行：

ro.sf.lcd_density=480

后重启，发现字体变大了！

2、  所以通过修改/system/build.prop是有效的，后面网上查了一下build.prop的过程，它是由android编译系统生成的文件，主要属性配置来源与三个方面：

①   build/tools/buildinfo.sh执行脚本，并输出到build.prop

②   把$(TARGET_DEVICE_DIR)/system.prop的内容追加到build.prop中

③   收集ADDITIONAL_BUILD_PROPERTIES中的属性，追加到build.prop中。

3、 通过修改

device\qcom\msm8916_64_slm755_meig_02\system.prop

添加一行：

ro.sf.lcd_density=480，编译系统 make –j8

4、 刚开始

out\target\product\msm8916_64_slm755_meig_02\system\build.prop

文件中出现了ro.sf.lcd_density=480可是后面又变回到原来的样子，ro.sf.lcd_density=480消失了！！不解！

5、 后来发现是因为在out\target\product\msm8916_64_slm755_meig_02\system\下面还有一个

文件：build.prop.bakforspec