如何在没有HDMI的情况下启动Qualcomm Snapdragon

Question

我有一个应用程序，它接收视频流，对其进行处理，并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。

重要的是，系统可以在不插入HDMI的情况下启动。但是，在未插入显示器的情况下启动系统时，启动过程陷入无限循环，似乎正在尝试启动视频/音频服务，失败，然后再次尝试。插入HDMI后，系统可以完成引导，然后继续进入主屏幕。这是我在没有HDMI的情况下尝试引导时，通过串口获得的永远循环的日志：

[ 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

我相信应该有一些方法来编辑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”。

虽然我已经研究了这些东西，但我不知道如何真正去实现它们，我不确定这是不是正确的道路。任何帮助都将不胜感激！

编辑:似乎通过编辑Android源代码来正确地完成这项工作的方法远远超出了我的工资等级，但一个简单的解决办法是购买一个模拟HDMI显示器的HDMI虚拟插头。基本上，它只是在它的寄存器中有EDID数据，并在操作系统最初查找它的显示器时将这些数据吐出来。

Answer 1

DisplayDevice.cpp带我找到了Virtual display composition

虚拟显示组合类似于外部显示组合。Hardware Composer (HWC)将输出写入缓冲区，提供完成栏，并将缓冲区发送给使用者(如视频编码器、GPU、CPU等)。如果显示流水线写入内存，则虚拟显示可以使用2D/阻击器或覆盖。

Virtual displays也解释了这一点：

SurfaceFlinger支持内置显示器(内置在电话或平板电脑中)、外部显示器(例如通过高清晰度接口连接的电视)以及一个或多个虚拟显示器，这些显示器可在系统内提供合成输出。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。

为了提供预期的输出缓冲器，必须连接虚拟显示设备。经过短暂的研究，我不太确定如何做到这一点，但当查看日志时……它似乎已经搞砸了，当它试图得到一个显示器，以显示启动动画。

则需要将该虚拟显示设备设置为主输出缓冲器。TYPE_HDMI = 2和TYPE_VIRTUAL = 5 ..。在Display.java中找到。

请随时发布更好的答案，以防您可以了解它是如何工作的。