如何在没有 HDMI 的情况下启动 Qualcomm Snapdragon

Question

我正在为运行 Android 的 Qualcomm Snapdragon 开发视频应用程序。我有一个应用程序，它接收视频流，对其进行处理，然后根据图像发送数据流。它还可以具有将图像显示到 HDMI 的模式，但这不是必需的。我还将我的应用配置为在启动时自动运行。

在没有插入 HDMI 的情况下可以启动系统很重要。但是，在没有插入显示器的情况下启动系统时，启动过程会陷入无限循环，似乎正在尝试启动视频/音频服务，失败，然后重试。插入 HDMI 后，系统能够完成启动，然后继续进入主屏幕。这是我通过串行获得的日志，当尝试在没有 HDMI 的情况下启动时，它会永远循环：

[ 22.471956] init: property_set("ro.boottime.audioserver", "22471598897") failed: property already set
[ 22.481207] init: property_set("ro.boottime.cameraserver", "22480859470") failed: property already set
[ 22.490533] init: property_set("ro.boottime.media", "22490197595") failed: property already set
[ 22.499191] init: property_set("ro.boottime.netd", "22498862751") failed: property already set
[ 22.531151] init: property_set("ro.boottime.wificond", "22530820772") failed: property already set
[ 22.983305] MSM-CPP cpp_init_hardware:1023 stream_cnt:0
[ 23.126367] init: property_set("ro.boottime.zygote", "23125974574") failed: property already set
[ 23.206157] MSM-CPP cpp_init_hardware:1023 stream_cnt:0
[ 23.561725] msm_qti_pp_get_rms_value_control, back not active to query rms be_idx:3
[ 23.573642] msm_voice_sound_focus_get: Error getting Sound Focus Params, err=-22
[ 23.580423] msm_voice_source_tracking_get: Error getting Source Tracking Params, err=-22
[ 23.588465] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 23.594484] msm_audio_sound_focus_get: Could not get copp idx for port_id=16385
[ 23.602184] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 23.608040] msm_audio_source_tracking_get: Could not get copp idx for port_id=16385
[ 23.616115] msm_voice_sound_focus_get: Error getting Sound Focus Params, err=-22
[ 23.623421] msm_voice_source_tracking_get: Error getting Source Tracking Params, err=-22
[ 23.631478] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 23.637464] msm_audio_sound_focus_get: Could not get copp idx for port_id=4101
[ 23.644995] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 23.651027] msm_audio_source_tracking_get: Could not get copp idx for port_id=4101
[ 23.658855] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 23.664939] msm_audio_sound_focus_get: Could not get copp idx for port_id=4103
[ 23.672444] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 23.678435] msm_audio_source_tracking_get: Could not get copp idx for port_id=4103
[ 23.688260] msm_pcm_volume_ctl_get substream runtime not found
[ 23.694029] msm_pcm_volume_ctl_get substream runtime not found
[ 23.699605] msm_pcm_volume_ctl_get substream runtime not found
[ 23.705037] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.712576] msm_pcm_volume_ctl_get substream runtime not found
[ 23.717709] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.725125] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.731802] msm_pcm_volume_ctl_get substream runtime not found
[ 23.737211] msm_pcm_volume_ctl_get substream or runtime not found
[ 23.744698] msm_pcm_volume_ctl_get substream runtime not found
[ 23.749964] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.757250] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.764110] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.770790] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.777327] msm_compr_audio_effects_config_get: stream or effects inactive
[ 23.784724] msm_compr_audio_effects_config_get: stream or effects inactive
[ 25.705018] init: property_set("ro.boottime.surfaceflinger", "25704640562") failed: property already set
[ 25.705499] init: Failed to bind socket 'pdx/system/vr/display/client': No such file or directory
[ 25.705779] init: Failed to bind socket 'pdx/system/vr/display/manager': No such file or directory
[ 25.706060] init: Failed to bind socket 'pdx/system/vr/display/vsync': No such file or directory
[ 26.052708] init: Unable to open '/sys/android_power/request_state': No such file or directory
[ 26.060404] init: Unable to write to '/sys/power/state': Invalid argument
[ 26.138413] init: property_set("ro.boottime.hwcomposer-2-1", "26138041187") failed: property already set
[ 26.534961] init: property_set("ro.boottime.audio-hal-2-0", "26534542802") failed: property already set
[ 27.048016] msm_qti_pp_get_rms_value_control, back not active to query rms be_idx:3
[ 27.057638] msm_voice_sound_focus_get: Error getting Sound Focus Params, err=-22
[ 27.064137] msm_voice_source_tracking_get: Error getting Source Tracking Params, err=-22
[ 27.072189] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 27.078398] msm_audio_sound_focus_get: Could not get copp idx for port_id=16385
[ 27.085828] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 27.092048] msm_audio_source_tracking_get: Could not get copp idx for port_id=16385
[ 27.099817] msm_voice_sound_focus_get: Error getting Sound Focus Params, err=-22
[ 27.107172] msm_voice_source_tracking_get: Error getting Source Tracking Params, err=-22
[ 27.115220] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 27.121482] msm_audio_sound_focus_get: Could not get copp idx for port_id=4101
[ 27.128760] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 27.135023] msm_audio_source_tracking_get: Could not get copp idx for port_id=4101
[ 27.142667] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 27.148883] msm_audio_sound_focus_get: Could not get copp idx for port_id=4103
[ 27.156218] msm_audio_get_copp_idx_from_port_id: Invalid FE, exiting
[ 27.162444] msm_audio_source_tracking_get: Could not get copp idx for port_id=4103
[ 27.171810] msm_pcm_volume_ctl_get substream runtime not found
[ 27.177051] msm_pcm_volume_ctl_get substream runtime not found
[ 27.182976] msm_pcm_volume_ctl_get substream runtime not found
[ 27.188378] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.195922] msm_pcm_volume_ctl_get substream runtime not found
[ 27.201188] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.208164] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.215088] msm_pcm_volume_ctl_get substream runtime not found
[ 27.220547] msm_pcm_volume_ctl_get substream or runtime not found
[ 27.227649] msm_pcm_volume_ctl_get substream runtime not found
[ 27.232647] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.239729] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.246622] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.253478] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.260348] msm_compr_audio_effects_config_get: stream or effects inactive
[ 27.267146] msm_compr_audio_effects_config_get: stream or effects inactive

我相信应该有某种方法来编辑 init.rc 文件以防止音频/视频服务在启动时运行，然后在启动后插入 HDMI 时在 ueventd 中注册某种“热插拔”。

虽然我研究了这些事情，但我对如何实际实施它们感到迷茫，我不确定这是否是正确的路径。任何帮助将不胜感激！

编辑：通过编辑 Android 源代码来正确执行此操作的方法似乎远高于我的工资等级，但一个简单的解决方法是购买一个模拟 HDMI 监视器的 HDMI 虚拟插头。基本上，它的寄存器中只有 EDID 数据，并在操作系统最初查找其显示时将其吐出。

Answer 1

DisplayDevice.cpp 已将我带到Virtual display composition：

虚拟显示组合类似于外部显示组合。虚拟显示合成和物理显示合成之间的区别在于，虚拟显示将输出发送到 Gralloc 缓冲区而不是屏幕。 Hardware Composer (HWC) 将输出写入缓冲区，提供完成围栏，并将缓冲区发送给消费者（例如视频编码器、GPU、CPU 等）。如果显示管道写入内存，则虚拟显示可以使用 2D/blitter 或叠加。

还有Virtual displays解释它：

SurfaceFlinger 支持内部显示器（内置在手机或平板电脑中）、外部显示器（例如通过 HDMI 连接的电视），以及一个或多个虚拟显示器，可在系统内提供复合输出。虚拟显示器可用于记录屏幕或通过网络发送屏幕。为虚拟显示器生成的帧被写入BufferQueue。

必须连接一个虚拟显示设备，才能提供预期的输出缓冲区。经过短暂的研究，我不确定如何实现这一点，但是在查看日志时......似乎在尝试显示时它已经搞砸了，以便显示启动动画。

该虚拟显示设备需要设置为主输出缓冲区。 我认为应该可以使用文件system.prop 或一些*.rc 文件或它可能引用的任何init.*.sh 来配置它。 TYPE_HDMI = 2 和 TYPE_VIRTUAL = 5 ... 在 Display.java 中找到。在插入或拔出 HDMI 电缆时，您正在寻找的事件似乎是 DisplayAdapter.DISPLAY_DEVICE_EVENT_CHANGED。

如果您能了解其工作原理，请随时发布更好的答案。