最近有個項目需要實現快速開機出攝像頭預覽（2s內），但是我的板子linux上的qt應用起來都要10s左右了，於是在硬件上增加了一個屏驅芯片TW8836，這是一個mcu，可以直接獲取攝像頭數據送到lcd顯示。
板子上電后首先由8836點亮屏幕並輸出攝像頭預覽，待arm起來后控制8836切換顯示，8836接受arm lvds信號並送到lcd顯示，同時8836將camera數據（bt656）回傳給arm.
由於我們這邊主要是搞arm，沒有更多的預留時間去熟悉研究8836這顆mcu的用法，但是我們板子上還有一顆當做看門狗的stm32，可以通過iic設置8836的寄存器，從而實現相應功能，最后硬件大致框圖如下
板子上電前期，stm32先通過iic控制8836輸出camera預覽，待arm起來后，再由arm通過iic控制8836顯示arm輸出的內容。這過程中就涉及到兩個主機公國iic控制同一個從機的邏輯。
首先驗證smt32單獨通過iic單獨控制8836，驗證ok。
其次驗證arm單獨通過iic單獨控制8836，驗證ok。
但是將stm32 、8836及arm都通過iic連接在一起的時候，stm32可以與8836通訊，但是arm無法與8836通訊。
對應log如下：
[root@t3_p3 ~]# insmod gt9xx_ts.ko [ 24.608866] kyleprint: >>> goodix_ts_init [ 24.613541] ctp_fetch_sysconfig_para: ctp_power_io is invalid. [ 24.621138] tab:-----------------ms 1---------------------- [ 24.627253] GTP9xx***CTP*** ctp_wakeup:status:0,ms = 0 [ 24.633091] GTP9xx***config_info.wakeup_gpio.gpio = 227 [ 24.690100] GTP9xx***CTP*** ctp_wakeup:status:1,ms = 0 [ 24.695742] GTP9xx***config_info.wakeup_gpio.gpio = 227 [ 24.720675] i2c-core: driver [gt9xx] using legacy suspend method [ 24.727331] i2c-core: driver [gt9xx] using legacy resume method [ 24.734093] GTP9xxctp_detect: addr = 45 [ 24.738550] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.747991] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.757244] i2c_test:I2C retry timeout, reset chip. [ 24.780260] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.789830] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.799080] i2c_test:I2C retry timeout, reset chip. [ 24.820227] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.829752] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.838982] i2c_test:I2C retry timeout, reset chip. [ 24.860384] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.869811] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.879086] i2c_test:I2C retry timeout, reset chip. [ 24.900415] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.909992] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 24.919239] i2c_test:I2C retry timeout, reset chip. [ 25.150324] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.159883] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.169112] i2c_test:get tw8836_id failed ret = -70 [ 25.380296] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.389787] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.399036] i2c_test:get tw8836_id failed ret = -70 [ 25.610448] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.620066] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.629189] i2c_test:get tw8836_id failed ret = -70 [ 25.840414] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.849863] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 25.859075] i2c_test:get tw8836_id failed ret = -70 [ 26.070362] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.079971] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.089269] i2c_test:get tw8836_id failed ret = -70 [ 26.300313] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.309776] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.319022] i2c_test:get tw8836_id failed ret = -70 [ 26.530240] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.539667] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.549098] i2c_test:get tw8836_id failed ret = -70 [ 26.760332] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.769763] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.779047] i2c_test:get tw8836_id failed ret = -70 [ 26.990276] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 26.999848] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 27.009101] i2c_test:get tw8836_id failed ret = -70 [ 27.220466] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 27.230077] sunxi_i2c_do_xfer()902 - [i2c2] incomplete xfer (status: 0x20, dev addr: 0x45) [ 27.239151] i2c_test:get tw8836_id failed ret = -70 [ 27.244752] ctp_detect:I2C connection might be something wrong
iic從設備沒有響應，只能用示波器抓波形觀察，發現sda數據項一直處於高電平無法拉低，但是在stm32與8836通訊的時候卻可以正常高低切換。
回想對比，發現問題的根本原因是，我在stm32操作完iic后沒有將scl和sda釋放，因為stm32那邊的iic走的是軟件模擬的方式，空閑狀態下SDA和SCL兩個io口都被我拉高了，導致arm這邊無法將電平拉低。
最后在stm iic部分，每次操作完iic就將SDA 和SCL釋放，設置成輸入狀態。
釋放io口后arm已經可以正常與8836通訊，能夠正常獲取到chip id 0x36
[ 686.617078] kyleprint: >>> goodix_ts_init [ 686.621729] ctp_fetch_sysconfig_para: ctp_power_io is invalid. [ 686.630192] goodix_ts_init:requst irq gpio fail! [ 686.635399] tab:-----------------ms 1---------------------- [ 686.635399] GTP9xx***CTP*** ctp_wakeup:status:0,ms = 0 [ 686.635399] GTP9xx***config_info.wakeup_gpio.gpio = 227 [ 686.690186] GTP9xx***CTP*** ctp_wakeup:status:1,ms = 0 [ 686.695816] GTP9xx***config_info.wakeup_gpio.gpio = 227 [ 686.721011] i2c-core: driver [gt9xx] using legacy suspend method [ 686.727638] i2c-core: driver [gt9xx] using legacy resume method [ 686.734423] GTP9xxctp_detect: addr = 45 [ 686.739420] i2c_test pass [ 686.950714] i2c_test: i= 1 get tw8836_id 0x00 ret 2 [ 686.956180] i2c_test: i= 1 get tw8836_id 0x36 ret 2 [ 687.170542] i2c_test: i= 2 get tw8836_id 0x00 ret 2 [ 687.176041] i2c_test: i= 2 get tw8836_id 0x36 ret 2 [ 687.390399] i2c_test: i= 3 get tw8836_id 0x00 ret 2 [ 687.395851] i2c_test: i= 3 get tw8836_id 0x36 ret 2 [ 687.610415] i2c_test: i= 4 get tw8836_id 0x00 ret 2 [ 687.615858] i2c_test: i= 4 get tw8836_id 0x36 ret 2 [ 687.830542] i2c_test: i= 5 get tw8836_id 0x00 ret 2 [ 687.835980] i2c_test: i= 5 get tw8836_id 0x36 ret 2 [ 688.050448] i2c_test: i= 6 get tw8836_id 0x00 ret 2 [ 688.055920] i2c_test: i= 6 get tw8836_id 0x36 ret 2 [ 688.270492] i2c_test: i= 7 get tw8836_id 0x00 ret 2 [ 688.275955] i2c_test: i= 7 get tw8836_id 0x36 ret 2 [ 688.490476] i2c_test: i= 8 get tw8836_id 0x00 ret 2 [ 688.495963] i2c_test: i= 8 get tw8836_id 0x36 ret 2 [ 688.710888] i2c_test: i= 9 get tw8836_id 0x00 ret 2 [ 688.716341] i2c_test: i= 9 get tw8836_id 0x36 ret 2 [ 688.930820] i2c_test: i= 10 get tw8836_id 0x00 ret 2 [ 688.936359] i2c_test: i= 10 get tw8836_id 0x36 ret 2