lk部分：（实现LCD兼容）
1. 函数定位
aboot_init()来到target_display_init()；
这就是高通原生lk LCD 兼容的关键所在。至于你需要兼容多少LCD 就在while（）设置了，具体代码就不跟下去了。
然后根据target中的不同文件来判断是否进入哪一个函数来处理：
target_display_init() 函数里有很重要函数就是gcdb_display_init();
如果平台支持屏幕最大个数自动检测，msm8953支持兼容两个屏。(GCDB：Global Component Database全局组件数据库)；
gcdb_display_init初始化pll_clk_func、power_func、bl_func等功能（指明相应的函数指针），初始化好之后就调用msm_display_init()函数。
在msm_display_init()里先Turn on panel，再Turn on backlight；
panel.power_func = mdss_dsi_panel_power; //turn on panel
panel.bl_func = mdss_dsi_bl_enable; //turn on backlight
函数指向相应的函数中去；
2. 打开lcd
/* Turn on panel */
1. 调用mdss_dsi_panel_power()中的regulator_enable()给L2、L6、L17供电
if (pdata->power_func)
ret = pdata->power_func(1, &(panel->panel_info));
2. 调用mdss_dsi_mipi_dfps_config函数：
if (pdata->dfps_func)
ret = pdata->dfps_func(&(panel->panel_info));
3. 调用mdss_dsi_panel_clock()
调用calculate_clock_config(pinfo)计算时钟配置和调用target_panel_clock(enable, pinfo)配置目标panel的时钟。
4. 分配并设置帧缓存：
msm_fb_alloc(&(panel->fb))和fbcon_setup(&(panel->fb))为帧缓冲器(frame buffer)分配内存。
5. 获取logo图片：
调用fetch_image_from_partition()从splash分区获取lk logo图片，如果splash分区没有满足要求的数据，就显示默认的logo。
6. DSI转HDMI：
if ((panel->dsi2HDMI_config) && (panel->panel_info.has_bridge_chip))
ret = panel->dsi2HDMI_config(&(panel->panel_info));
7. msm_display_config()函数：
7.1 mdss_dsi_phy_init()
mdss_dsi_phy_init(&mipi_pinfo,MIPI_DSI0_BASE, DSI0_PHY_BASE);
if(pinfo->mipi.dual_dsi)
如果有两个MIPI DSI接口MIPI_DSI0和MIPI_DSI1就调用两次mdss_dsi_phy_init()，msm8909只有MIPI_DSI0，MSM8994等有两个DSI接口。
mdss_dsi_phy_init(&mipi_pinfo,MIPI_DSI1_BASE, DSI1_PHY_BASE);
7.2 ret = mdss_dsi_host_init(mipi, mipi->dual_dsi, mipi->broadcast);
初始化DSI接口的host控制器。
7.3 调用if (panel->pre_init_func) {}函数：
static int mdss_dsi_panel_pre_init(void)
{
intret = NO_ERROR;
if(panelstruct.paneldata->panel_lp11_init) {
ret= mdss_dsi_panel_reset(1);
if(ret) {
dprintf(CRITICAL,"panel reset failed
");
returnret;
}
}
if(panelstruct.paneldata->panel_init_delay)
udelay(panelstruct.paneldata->panel_init_delay);
dprintf(SPEW,"Panel pre init done
");
returnret;
}
因为panelstruct.paneldata->panel_lp11_init在init_panel_data()函数赋值为1，所以调用mdss_dsi_panel_reset()根据reset时序来复位panel。
8. ret = msm_display_on();
主要部分：
case MIPI_VIDEO_PANEL:
dprintf(INFO, "Turn on MIPI_VIDEO_PANEL.
");
ret = mdp_dsi_video_on(pinfo);
if (ret)
goto msm_display_on_out;
ret = mdss_dsi_post_on(panel);
if (ret)
goto msm_display_on_out;
ret = mipi_dsi_on(pinfo);
if (ret)
goto msm_display_on_out;
break;
8.1 调用mdp_dsi_video_on()使能DSI VIDEO
8.2 mdss_dsi_post_on()使用初始化命令来初始化panel
8.3 mipi_dsi_on()
9. 打开背光：
/* Turn on backlight */
if (pdata->bl_func)
ret = pdata->bl_func(1);
3. 增加一个panel需要做的事：
1、在gcdb_display_init()函数中有一个函数oem_panel_select()函数：
（这个函数需要做的工作是：主要是识别不同IC，赋值给参数panel_id，panel_id的使用在同一文件中的 init_panel_data()函数中。）
pan_type = oem_panel_select(panel_name, &panelstruct, &(panel.panel_info),
&dsi_video_mode_phy_db);
2、uint32_t hw_id = board_hardware_id();
//判断是高通哪一款平台，这里不需要看，hw_id是不需要管的，因为在下面语句中会直接跳到init_panel_data函数中来
3、在oem_panel_select()函数中需要根据你的hw_id来确定使用哪一款的LCD；
panel_override_id = panel_name_to_id(supp_panels,
ARRAY_SIZE(supp_panels), panel_name);
supp_panels是struct panel_list，如果要增加一个panel就需要在这里增加一个supp_panels，例如：
static struct panel_list supp_panels[] = {
{"truly_1080p_video", TRULY_1080P_VIDEO_PANEL},
{"truly_1080p_cmd", TRULY_1080P_CMD_PANEL},
{"r69006_1080p_video", R69006_1080P_VIDEO_PANEL},
{"r69006_1080p_cmd", R69006_1080P_CMD_PANEL},
{"truly_wuxga_video", TRULY_WUXGA_VIDEO_PANEL},
{"nt35523_720p_video", NT35523_720P_VIDEO_PANEL},
{"a914_nhd_video", A914_NHD_VIDEO_PANEL},
};
4、在这个枚举中也需要增加相应的panel：
/*---------------------------------------------------------------------------*/
enum {
TRULY_1080P_VIDEO_PANEL,
TRULY_1080P_CMD_PANEL,
R69006_1080P_VIDEO_PANEL,
R69006_1080P_CMD_PANEL,
TRULY_WUXGA_VIDEO_PANEL,
NT35523_720P_VIDEO_PANEL,
A914_NHD_VIDEO_PANEL,
UNKNOWN_PANEL
};
if (panel_name) {
panel_override_id = panel_name_to_id(supp_panels,
ARRAY_SIZE(supp_panels), panel_name);
if (panel_override_id < 0) {
dprintf(CRITICAL, "Not able to search the panel:%s
",
panel_name + strspn(panel_name, " "));
} else if (panel_override_id < UNKNOWN_PANEL) {
/* panel override using fastboot oem command */
panel_id = panel_override_id;
dprintf(INFO, "OEM panel override:%s
",
panel_name + strspn(panel_name, " "));
goto panel_init;
}
}
……
panel_init:
/*
* Update all data structures after 'panel_init' label. Only panel
* selection is supposed to happen before that.
*/
pinfo->pipe_type = MDSS_MDP_PIPE_TYPE_RGB;
return init_panel_data(panelstruct, pinfo, phy_db);
确保能直接跳到panel_init函数中来；
5、同样来到init_panel_data()函数中来：
在这里也需要增加一个panel：（当然了，要增加相应的头文件#include "include/panel_a914_nhd_video.h"这个头文件是LCM供应商给的文件，一般来说都要自己根据时序图来参照）
case TRULY_WUXGA_VIDEO_PANEL:
panelstruct->paneldata = &truly_wuxga_video_panel_data;
panelstruct->paneldata->panel_with_enable_gpio = 1;
panelstruct->panelres = &truly_wuxga_video_panel_res;
panelstruct->color = &truly_wuxga_video_color;
panelstruct->videopanel = &truly_wuxga_video_video_panel;
panelstruct->commandpanel = &truly_wuxga_video_command_panel;
panelstruct->state = &truly_wuxga_video_state;
panelstruct->laneconfig = &truly_wuxga_video_lane_config;
panelstruct->paneltiminginfo
= &truly_wuxga_video_timing_info;
panelstruct->panelresetseq
= &truly_wuxga_video_panel_reset_seq;
panelstruct->backlightinfo = &truly_wuxga_video_backlight;
pinfo->mipi.panel_on_cmds
= truly_wuxga_video_on_command;
pinfo->mipi.num_of_panel_on_cmds
= TRULY_WUXGA_VIDEO_ON_COMMAND;
pinfo->mipi.panel_off_cmds
= truly_wuxga_video_off_command;
pinfo->mipi.num_of_panel_off_cmds
= TRULY_WUXGA_VIDEO_OFF_COMMAND;
memcpy(phy_db->timing,
truly_wuxga_14nm_video_timings, MAX_TIMING_CONFIG * sizeof(uint32_t));
pinfo->dfps.panel_dfps = truly_wuxga_video_dfps;
pinfo->mipi.signature = TRULY_WUXGA_VIDEO_SIGNATURE;
break;
case A914_NHD_VIDEO_PANEL:
panelstruct->paneldata = &a914_nhd_video_panel_data;
panelstruct->panelres = &a914_nhd_video_panel_res;
panelstruct->color = &a914_nhd_video_color;
panelstruct->videopanel = &a914_nhd_video_video_panel;
panelstruct->commandpanel = &a914_nhd_video_command_panel;
panelstruct->state = &a914_nhd_video_state;
panelstruct->laneconfig = &a914_nhd_video_lane_config;
panelstruct->paneltiminginfo
= &a914_nhd_video_timing_info;
panelstruct->panelresetseq
= &a914_nhd_video_panel_reset_seq;
panelstruct->backlightinfo = &a914_nhd_video_backlight;
pinfo->mipi.panel_on_cmds
= a914_nhd_video_on_command;
pinfo->mipi.num_of_panel_on_cmds
= A914_NHD_VIDEO_ON_COMMAND;
pinfo->mipi.panel_off_cmds
= a914_nhd_video_off_command;
pinfo->mipi.num_of_panel_off_cmds
= A914_NHD_VIDEO_OFF_COMMAND;
memcpy(phy_db->timing,
a914_nhd_video_timings, MAX_TIMING_CONFIG * sizeof(uint32_t));
pinfo->mipi.signature = A914_NHD_VIDEO_SIGNATURE;
break;
6、调整背光：
在gcdb_display_init()函数中有一个函数指针mdss_dsi_bl_enable：
这个函数是用来调整背光的和使能背光的，通过PWM来作用：（具体要看原理图）
static int mdss_dsi_bl_enable(uint8_t enable)
{
int ret = NO_ERROR;
ret = panel_backlight_ctrl(enable);
if (ret)
dprintf(CRITICAL, "Backlight %s failed
", enable ? "enable" :
"disable");
return ret;
}
static uint32_t panel_backlight_ctrl(uint8_t enable)
{
uint32_t ret = NO_ERROR;
if (panelstruct.backlightinfo)
ret = target_backlight_ctrl(panelstruct.backlightinfo, enable);
return ret;
}
所以bootloader的背光是通过target_backlight_ctrl()控制的，找到该项目的这个函数修改：
wled_backlight_ctrl；
7、更改LCD的参数：
LCD的一些参数：
VBPD(verticalback porch)：表示在一帧图像开始时，垂直同步信号以后的无效的行数。
VFPD(verticalfront porch)：表示在一帧图像结束后，垂直同步信号以前的无效的行数。
VSPW(verticalsync pulse width)：表示垂直同步脉冲的宽度，用行数计算。
HBPD(horizontal back porch)：表示从水平同步信号开始到一行的有效数据开始之间的VCL的个数。
HFPD(horizontal front porch)：表示一行的有效数据结束到下一个水平同步信号开始 之间的VCLK的个数。
HSPW(horizontalsync pulse width)：表示水平同步信号的宽度，用VCLK计算。