Disable Weston video playback offset

-

現在目標與狀況

    目標

    • Disable Weston video playback
    • User hardware decode

    遇到狀況

    • Enable Weston video playback normally
      • gst-launch-1.0 filesrc location=/home/root/demo.mp4 ! \
qtdemux name=d d.video_0 ! queue ! h264parse ! vpudec ! \
queue ! waylandsink
    • Disable Weston video playback offset
      • gst-launch-1.0 -v \
filesrc location=/home/root/demo.mp4 ! \
qtdemux name=d d.video_0 ! queue ! h264parse ! \
vpudec ! glimagesink

驗證分析

  • 同一支影片、同一個 decoder，在不同video sink，行為不同
  • 更換video sink
    • glimagesink: 是 OpenGL 視窗/GL render 路徑
    • kmssink: 是直接走 DRM/KMS plane 的路徑
  • 如果要避開 Weston，又想低 CPU，應該要是decoder → KMS plane
  • 簡單測試kmssink
    • gst-launch-1.0 -v videotestsrc ! kmssink
        
# 發現顯示 Caught SIGSEGV，所以kmssink有bug
  • 用 modetest 去看DRM支援什麼
    • modetest -M imx-drm
    
# formats: XR24 AR24 RG16 XB24 AB24 RX24 RA24 AR15 XR15 AB15 XB15 BG16
# 沒有 NV12 / NV16
# vpudec 解碼輸出影像格式是 NV12，DRM plane不支援顯示 NV12
  • 不使用vpudec,指定輸出格式丟到kmssink
    • videotestsrc ! videoconvert ! video/x-raw,format=BGRx,width=1280,height=800 ! kmssink
    
# 還是crash
  • 使用gdb debug
    • gdb --args gst-launch-1.0 --gst-disable-segtrap -v \
videotestsrc ! videoconvert ! \
video/x-raw,format=BGRx,width=1280,height=800 ! \
kmssink driver-name=imx-drm plane-id=29 

# --args : 後續為GStreamer指令
# --gst-disable-segtrap : GStreamer 不攔截 SIGSEGV

    (gdb) handle SIGSEGV stop print nopass
    
# stop:當GStreamer收到 SIGSEGV 時停止執行
# print:收到 SIGSEGV 時 GDB 會打印信號信息
# nopass:GStreamer不會自行處理或崩潰，由 GDB 接管

    (gdb) run
# 正式啟動GStreamer
#其中發現
Thread 2 "videotestsrc0:s" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xffffbeed91f0 (LWP 4051)]
strcmp () at ../sysdeps/aarch64/strcmp.S:64

(gdb) bt
#0  strcmp () at ../sysdeps/aarch64/strcmp.S:64
#1  0x0000ffffbef8117c in ?? () from /usr/lib/gstreamer-1.0/libgstkms.so
#2  0x0000000000652df0 in ?? ()
#3  0x657361625f747367 in ?? ()

# 表示libgstkms.so 裡某個函式呼叫 strcmp() 時出了問題


    (gdb) thread apply all bt
# 檢視其他thread是否有問題
# 顯示 :
	Thread 2
		停在strcmp() → 這就是出事的 thread
	Thread 1 / Thread 3
    	在等待

  • 確認是strcmp()問題，回到gstreamer1.0-plugins source找尋strcmp()
    • grep -R "strcmp *(" -n sys/kms
sys/kms/gstkmssink.c:496:  if (strcmp (get_imx_drm_device_name(), "DPU") == 0) {
sys/kms/gstkmssink.c:747:    if (!strcmp (property->name, prop_name)) {
sys/kms/gstkmssink.c:1446:      if (!strcmp(prop->name, "dtrc_table_ofs")) {
sys/kms/gstkmssink.c:1670:    if (!strcmp(prop->name, "dtrc_table_ofs") && dtrc_table_ofs) {
sys/kms/gstkmssink.c:1696:    if (!strcmp(prop->name, "alpha")) {
sys/kms/gstkmssink.c:1948:        if (!strcmp(prop->name, "HDR_SOURCE_METADATA")) {
sys/kms/gstkmssink.c:2020:  if (strcmp (get_imx_drm_device_name(), "DPU") == 0) {

  • 確認是strcmp()問題，回到gstreamer1.0-plugins source找尋strcmp()
    • grep -R "strcmp *(" -n sys/kms
sys/kms/gstkmssink.c:496:  if (strcmp (get_imx_drm_device_name(), "DPU") == 0) {
sys/kms/gstkmssink.c:747:    if (!strcmp (property->name, prop_name)) {
sys/kms/gstkmssink.c:1446:      if (!strcmp(prop->name, "dtrc_table_ofs")) {
sys/kms/gstkmssink.c:1670:    if (!strcmp(prop->name, "dtrc_table_ofs") && dtrc_table_ofs) {
sys/kms/gstkmssink.c:1696:    if (!strcmp(prop->name, "alpha")) {
sys/kms/gstkmssink.c:1948:        if (!strcmp(prop->name, "HDR_SOURCE_METADATA")) {
sys/kms/gstkmssink.c:2020:  if (strcmp (get_imx_drm_device_name(), "DPU") == 0) {


    (gdb) info registers
# 顯示目前 CPU register的內容

x0 0xdf8475800 60000000000
x1 0xffffbef86390 281473885692816 
x2 0xffffb8000080 281473768751232 
x3 0xffffb80008d0 281473768753360
...
...
...



    (gdb) x/16i $pc
# 反組譯（disassemble）目前程式執行machine Code

0xffffbf326d18 <strcmp+24>: ldr x2, [x0], #8 
0xffffbf326d1c <strcmp+28>: ldr x3, [x1], #8
...
...
...

  • 依造上述 (gdb) info registers 和 (gdb) (gdb) x/16i $pc 的內容
    • strcmp(a, b);
x0 = a
x1 = b
call strcmp

所以實際上執行strcmp(x0, x1)
x0 = 0xdf8475800   (60000000000) 看起來很不像合法字串位址
  • 所以結合source找尋strcmp() 的結果，像問題點只有
    • sys/kms/gstkmssink.c:496:  if (strcmp (get_imx_drm_device_name(), "DPU") == 0) {
sys/kms/gstkmssink.c:2020:  if (strcmp (get_imx_drm_device_name(), "DPU") == 0) {
  • 查 get_imx_drm_device_name() 的實作
    • get_imx_drm_device_name (void){
const gchar * device;
...
if (strstr (entry->d_name, "dpu@")) {
  device = "DPU";
  break;
}
if (strstr (entry->d_name, "dcss@")) {
  device = "DCSS";
  break;
}
...
return device;
}
  • i.MX 8M Mini Applications Processor Reference Manual
      • 1.4.11 Display Interfaces
        The chip has the following display support:
          • LCDIF Display Controller:
          • Supports one layer
          • Supports up to 1920x1200p60 display through MIPI DSI
          • MIPI Interface:
          • 4-lane MIPI CSI interface
          • 4-lane MIPI DSI interface
          • CSI Interface:
          • CSI is a simple camera interface which is used to capture the MIPI CSI input and
        save the pixels into memory

解決方式

    1. 修正初始化
      2.  
      const gchar * device = NULL;
    
找得到 dpu@ → 回 "DPU"
找得到 dcss@ → 回 "DCSS"
找不到 → 回 NULL

讓程式變成一個可被程式判斷和處理狀態

    2. 補上LCDIF
      3.  
      if (strstr (entry->d_name, "dpu@")) {
	device = "DPU";
	break;
}

if (strstr (entry->d_name, "dcss@")) {
	device = "DCSS";
	break;
}
    
if (strstr (entry->d_name, "lcdif@")) {
	device = "LCDIF";
	break;
}

    3. 避免 crash
      4.  
      g_strcmp0(get_imx_drm_device_name(), "DPU") == 0

g_strcmp0(a, b) 和 strcmp(a, b) 類似，但差別在：
它允許 a 或 b 是NULL
不會因為NULL直接crash只會回傳「不相等」

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