Qualcomm platform LCM summary

The following figures are the most recent examples of our own modules LCM Some conclusions of , At present, it is only partially completed , And the description is not particularly in place , It will be updated and modified in the future .

The first one is LCM Overall migration framework and component diagram . It introduces LCM The steps and key points of the driving segment and debugging screen .

branch lk and kernel Two parts , What exactly .c, How to add a new screen , General steps and methods .

 

The second figure is the initialization flow chart of the screen , It is divided into lk and kernel Two parts .Lk Part of it is as follows :

When the system is up, it will call bootable/bootloader/lk/app/aboot/aboot.c, In this function aboot_init() Function to call the display initialization function target_display_init(), Call... In this function gcdb_display_init().

  One of the most important functions in this function is oem_panel_select(), It's defined in oem_panel.c in , It is based on Qualcomm's private code hw_id To decide which one you use LCD, And put panel Relevant data information is filled into the data structure --init_panel_data(),gcdb_display_init() After the execution of oem_panel_select() Be sure to use panel and panel After the relevant information , A series of values related to this are assigned through the function pointer panel Related functions , Include pll, Backlight ,clk, Initialization and enabling functions related to power supply , In order to call... Below .

meanwhile , Start execution   A series of screen initialization processes . First step , Access to electricity , perform pdata->power_func, Open some ldo, Enable some system power , Pull it higher gpio, Make the screen powered , And do it on the screen inside reset, The function called is target_panel_reset(), In the face reset The pins are operated high and low . Then enable the clock , call pdata->clk_func, Then do some enabling pll, Distribute framebuffer, adopt fbcon_setup(&(panel->fb)) Function to set the global pointer such as the resolution and display address of the record display . Next into msm_display_config() Function for LVDS_PANEL,MIPI_VIDEO_PANEL,MIPI_CMD_PANEL Etc dsi and mipi To configure .

After some columns dsi Parameter set last call mdss_dsi_panel_initialize(), Use mdss_dsi_cmds_tx() towards lcm Of driver ic Sent initialization code . And decide , If target_panel_auto_detect_enabled() Open the conversation , Using the Qualcomm platform lcm read_id function mdss_dsi_read_panel_signature() Conduct id Read .

After completing this series of operations, execute msm_display_on(), Lighting screen , The last stage calls pdata->bl_func(1) Turn on the backlight . So the whole LK Of lcm Initialization is complete .LK The initialization flow chart of is as follows .        

Next is kernel Stage LCM The initialization process .

kernel Stage , First, three platform devices will be registered in the driver ,msm_fb,mdp,mipi_dsi.mdp The module is Qualcomm's internal display control chip ,mipi_dsi It is a transport protocol layer device ,msm_fb It is the driving device of Qualcomm graphics card .

The first thing to execute is mdp Driven probe, Carry out hardware resources including clock , interrupt ,iommu, Bus ,DMA The initialization , Register some interfaces for fb Use of equipment .mdp Initialize after initialization dsi controller , stay mdss_dsi_ctrl_probe Function , A function was called mdss_ds_config_panel, In this function , Get by name matching panel Device node , If there is no match, call msm-mtp.dtsi Preset panel device node.

Next, execute the function dsi_panel_device_register() register panel_device Device node . In this register function , I'm sure it's DSI_VIDEO_MODE still MIPI_CMD_MODE, Obtained some resources such as gpio,regulatot,dsi-lane Relevant information , The important thing is that it registers a event_handler：mdss_dsi_event_handler, This event handler function will accept all kinds of... From other layers event Events include lighting , Turn off the screen, etc . Also through this event_handler,dsi Driver layer and fb layer ,mdp Layer to communicate .

And then execute mdss_dsi_panel_init Function panel The initialization . This function parses dtsi The file gets the name of the screen , The resolution of the , Physical dimensions ,dsi type ,porch Parameters , Color format , Initialization instruction , Backlight mode and other parameters , And fill them in one by one pinfo In this structure , And registered some on off , Set the backlight , Select operating functions such as mode . Next is mdss_fb Initialization of the device , stay mdss_fb_probe Function , By calling mfd->mdp.init_fnc To initialize mdp, adopt lcd_backlight_registered() To register the backlight driver .

When the system starts animation , Will call functions mdss_fb_open open fb controller , It's going to execute mdss_fb_blank_sub() And pass in FB_BLANK_UNBLANK event Parameters , perform mdss_fb_blank_unblank() function . In this function , By calling mfd->mdp.on_fnc() Yes mdp In drive on_fnc function , Namely mdp3_ctrl_on() function , This function moves forward dsi In drive event handler Send three events MDSS_EVENT_LINK_READY,MDSS_EVENT_UNBLANK,MDSS_EVENT_PANEL_ON call mdss_dsi_panel Driving medium mdss_dsi_on().

The configuration is executed inside dsi, Access to electricity ,reset, Send instructions to operate in a series to light up the screen . such kernel Part of the screen initialization is completed .

The picture below is KERNEL Initialization flow chart of the phase .

 

 

The fourth picture , It is the data transmission diagram of lighting screen and extinguishing screen from upper layer to bottom layer .

If you want to turn off the screen , The upper layer will call PowerManagerService Methods provided . The calling relationship of the whole process is goToSleep->goToSleepInternal-> updatePowerStateLocked->updateDisplayPowerStateLocked->

requestPowerState->sendUpdatePowerStateLocked->mHandler.sendMessage(msg)-> updatePowerState->animateScreenStateChange->setScreenState->scheduleScreenUpdate->

postScreenUpdateThreadSafe->mPhotonicModulator.setState->mLock.notifyAll-> mBlanker.requestDisplayState->initPowerManagement->callbacks.onDisplayStateChange->

setHalAutoSuspendModeLocked->nativeSetAutoSuspend

  The last to nativeSetAutoSuspend() This local method , Is in

frameworks/base/services/jni/com_android_server_power_PowerManagerService.cpp

Called , Call the autosuspend_enable(), This function will go to /sys/power/state Node

mem.

  This node , Is in kernel/kernel/power/main.c Created in sysfs The file nodes , Once a value is written into it, the corresponding store function . Off screen , The upper layer writes mem, Called store In the middle of suspend function , Then the system will go suspend technological process . Pass to the screen , stay msm_fb Call in system suspend function ,

After some column calls , Go to the mdss_fb_blank_blank(), call mfd->mdp.off_fnc, call mdp_ctrl.c

Of mdp_ctrl_off function , therefore panel->set_backlight(panel, 0) Turn off the backlight , By sending

MDSS_EVENT_BLANK to dsi In drive event_handler, call mdss_dsi_blank() Perform a series of operations to power off the screen . In this way, the whole screen extinguishing process is completed .

  If the screen is on , Also from PowerManagerService Provide methods wake up, Finally call jni Of autosuspend_disable(), Go to /sys/power/state Node on, Last call suspend Process Lighting screen .

  The flow chart is shown below .

    

                    

 

 

Picture 5 , It summarizes how the backlight adjustment is transmitted from the upper layer to the bottom layer .

When the user is on the mobile phone setting-display-backlights When adjusting the backlight , The system will call

packages\apps\Settings\src\com\android\settings\BrightnessPreference.java To achieve . Set the brightness adjustment range here 0-255, adopt powermanagerservice.java The interface of setBrightness Implementation services . This method is defined in LightService.java in , call setBrightness()--->setLightLocked()--->setLight_native().

This local method is in frameworks\base\services\jni\com_android_server_LightsService.cpp achieve . Under this file ,init_native Function , call hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module) obtain lights Hardware abstraction layer module lights.default.so And load , call hall Layer function devices->lights[light]->set_light(devices->lights[light],&state) Set brightness .hall The code of the layer is hardware/qcom/display/liblight/lights.c.

In this, we have realized open_lights,close_lights,rgb_to_brightness Such as function . The key is , When adjusting the brightness , Will call the set_light_backlight(), adopt write_int Go to /sys/class/leds/lcd-backlight/brightness Write value . This file node is located in kernel Layer creation .kernel layer , stay Mdss_dsi_panel.c In the document , There is a backlight control function static void mdss_dsi_panel_bl_ctrl(struct mdss_panel_data *pdata,u32 bl_level), The parameter backlight value is through this bl_level For adjustment .

After one layer of call , In fact, kernel/drivers/leds/Led-class.c Created in the sysfs The file nodes /sys/class/leds/lcd-backlight/brightness, And in store Function , Save the current brightness value to led_cdev->brightness variable , Layer by layer to the drive bl_level. such , The transmission of backlight adjustment values from the upper layer to the bottom layer is formed .

The above pictures , In general, it summarizes LCM The driving part and some upper level relations , technological process . This sort of arrangement is quite helpful for your understanding and familiarity with the module . With the deepening of the work , I will continue to supplement and improve this document , Hope to achieve good results in practical work .