平台：mt6582 + Android 4.4
前面就说过，在mtk代码中支持屏是可兼容的，通过调用驱动中的compare_id函数来匹配驱动和屏，这里来细看一下代码。
1. LK部分（mediatek/platform/mt6582/lk/disp_drv.c）
OOL DISP_DetectDevice(void)
{//LCD_STATUS ret;DISP_LOG("shi=>%s, %d\n", __func__, __LINE__);lcm_drv = disp_drv_get_lcm_driver(NULL);if (NULL == lcm_drv){printk("%s, disp_drv_get_lcm_driver() returns NULL\n", __func__);return FALSE;}disp_dump_lcm_parameters(lcm_params);return TRUE;
}在DISP_DetectDevice函数中调用了disp_drv_get_lcm_driver。
const LCM_DRIVER *disp_drv_get_lcm_driver(const char *lcm_name)
{LCM_DRIVER *lcm = NULL;printk("[LCM Auto Detect], we have %d lcm drivers built in\n", lcm_count);printk("[LCM Auto Detect], try to find driver for [%s]\n", (lcm_name==NULL)?"unknown":lcm_name);if(lcm_count ==1){// we need to verify whether the lcm is connected// even there is only one lcm type definedlcm = lcm_driver_list[0];lcm->set_util_funcs(&lcm_utils);lcm->get_params(&s_lcm_params);u4IndexOfLCMList = 0;lcm_params = &s_lcm_params;lcm_drv = lcm;
/*disp_drv_init_ctrl_if();disp_drv_set_driving_current(lcm_params);disp_drv_init_io_pad(lcm_params);if(lcm_drv->compare_id){if(LCM_TYPE_DSI == lcm_params->type){init_dsi(FALSE);}if(lcm_drv->compare_id() == TRUE){printk("[LCM Specified] compare id success\n");isLCMFound = TRUE;}else{printk("[LCM Specified] compare id fail\n");printk("%s, lcm is not connected\n", __func__);if(LCM_TYPE_DSI == lcm_params->type)DSI_Deinit();}}else
*/{isLCMFound = TRUE;}printk("[LCM Specified]\t[%s]\n", (lcm->name==NULL)?"unknown":lcm->name);goto done;}else{unsigned int i;for(i = 0;i < lcm_count;i++){lcm_params = &s_lcm_params;lcm = lcm_driver_list[i];printk("[LCM Auto Detect] [%d] - [%s]\t", i, (lcm->name==NULL)?"unknown":lcm->name);lcm->set_util_funcs(&lcm_utils);memset((void*)lcm_params, 0, sizeof(LCM_PARAMS));lcm->get_params(lcm_params);disp_drv_init_ctrl_if();disp_drv_set_driving_current(lcm_params);disp_drv_init_io_pad(lcm_params);if(lcm_name != NULL){if(!strcmp(lcm_name,lcm->name)){printk("\t\t[success]\n");isLCMFound = TRUE;u4IndexOfLCMList = i;lcm_drv = lcm;goto done;}else{printk("\t\t[fail]\n");}}else {if(LCM_TYPE_DSI == lcm_params->type){init_dsi(FALSE);MASKREG32(DSI_BASE + 0x10, 0x2, 0x2);}if(lcm->compare_id != NULL && lcm->compare_id()){printk("\t\t[success]\n");isLCMFound = TRUE;lcm_drv = lcm;u4IndexOfLCMList = i;goto done;}else{lcm_drv = lcm;if(LCM_TYPE_DSI == lcm_params->type){DSI_Deinit();DSI_PHY_clk_switch(false);}printk("\t\t[fail]\n");}}}}
done:if(LCM_TYPE_DSI == lcm_params->type){int ret = 0;unsigned int data_array[3];char buffer[4];init_dsi(FALSE);MASKREG32(DSI_BASE + 0x10, 0x2, 0x2);data_array[0] = 0x00043700;DSI_set_cmdq(data_array, 1, 1);ret = DSI_dcs_read_lcm_reg_v2(0x0A, &buffer,1);if(ret == 0){isLCMConnected = 0;printk("lcm is not connected\n");}else{isLCMConnected = 1;printk("lcm is connected\n");}DSI_Deinit();}return lcm_drv;
}如果lcm_count值为1，那么直接获取lcm_driver_list这个数组的第一个元素并把它赋值给一个全局变量lcm_drv，调用屏相关的set_util_funcs和get_params函数，所以如果只有一个屏驱动话，那是很简单的，也不用去匹配，直接拿来用就是了。
如果lcm_count值不为1呢，也就是有多个屏驱动呢，那么来看看是如何匹配的。
首先是for循环，依次遍历lcm_driver_list这个数组，如果lcm_name这个变量不为NULL，那么直接匹配lcm_name和屏驱动中的name字段是否相同，如果匹配成功，也就找到了相应的屏驱动，但是需要注意的是在LK中，这个变量值是为空的，有DISP_DetectDevice函数为证，所以说LK中肯定不会走这部分代码。那么是接下来的else部分，在else代码中，首先是判断屏驱动中的compare_id是否为空，如果不空的话，还会调用compare_id函数来匹配屏和驱动，如果两者都满足，那说明找到了合适的驱动，否则继续循环。所以匹配屏和驱动还是靠驱动中的compare_id函数来实现的。
注意：这里会有一个问题，如果是多个屏驱动的话，当前面都没有匹配成功的话，将使用最后一个屏驱动，请看代码：
lcm_drv = lcm;
if(LCM_TYPE_DSI == lcm_params->type){DSI_Deinit();DSI_PHY_clk_switch(false);
}
printk("\t\t[fail]\n");2. kernel部分（mediatek/platform/mt6582/kernel/drivers/video/disp_hal.c）
LK部分代码看完了，那么再来看kernel部分。
const LCM_DRIVER *disphal_get_lcm_driver(const char *lcm_name, unsigned int *lcm_index)
{LCM_DRIVER *lcm = NULL;bool isLCMFound = false;printk("[LCM Auto Detect], we have %d lcm drivers built in\n", lcm_count);printk("[LCM Auto Detect], try to find driver for [%s]\n", (lcm_name==NULL)?"unknown":lcm_name);if(lcm_count == 1){// we need to verify whether the lcm is connected// even there is only one lcm type definedlcm = lcm_driver_list[0];lcm->set_util_funcs(&lcm_utils);*lcm_index = 0;printk("[LCM Specified]\t[%s]\n", (lcm->name==NULL)?"unknown":lcm->name);isLCMFound = true;goto done;}else{int i;for(i = 0;i < lcm_count;i++){lcm = lcm_driver_list[i];printk("[LCM Auto Detect] [%d] - [%s]\t", i, (lcm->name==NULL)?"unknown":lcm->name);lcm->set_util_funcs(&lcm_utils);memset((void*)&s_lcm_params, 0, sizeof(LCM_PARAMS));lcm->get_params(&s_lcm_params);disphal_init_ctrl_if();LCD_Set_DrivingCurrent(&s_lcm_params);LCD_Init_IO_pad(&s_lcm_params);if(lcm_name != NULL){if(!strcmp(lcm_name,lcm->name)){printk("\t\t[success]\n");*lcm_index = i;isLCMFound = true;goto done;}else{printk("\t\t[fail]\n");}}else {if(LCM_TYPE_DSI == lcm_params->type){init_dsi(FALSE);}if(lcm->compare_id != NULL && lcm->compare_id()){printk("\t\t[success]\n");isLCMFound = true;*lcm_index = i;goto done;}else{if(LCM_TYPE_DSI == lcm_params->type)DSI_Deinit();printk("\t\t[fail]\n");}}}}
done:if (isLCMFound){memset((void*)&s_lcm_params, 0, sizeof(LCM_PARAMS));lcm->get_params(&s_lcm_params);return lcm;}elsereturn NULL;
}lcm=1-hx8389b_qhd_dsi_vdo这部分代码其实同LK的差不多，只是参数lcm_name字段就有可能不为空，即在LK中已经找到了合适的屏驱动，kernel中就不用再去匹配了。
