根据上一篇文章中的结论：如果在xbl阶段希望修改pmic相关的gpio，可以查看这个gpio是否已经有功能对其进行初始化。那么需要考虑一种情况：如果这个gpio从未被用过呢？因此本篇就是从根本上解决这个问题
根据高通文档可以得到的信息：
1.本平台最终是通过解析pm.dtsi这个设备树来进行gpio的初始化的
2.该设备树中的节点，在pm_sbl_boot_oem.c中进行解析
代码分析：
根据示例PM_CLK_ENABLE PM_BUSID_0 PMIC_A PM_CLK_RF_1 PM_TRUE，可以知道在pm.dtsi内要如何添加一个gpio的信息
sw-config {compatible = "qcom,pm-sw";// verbose: Set to TRUE will output verbose PON reason into uart log.//Set to 2 will output verbose PON reason and raw data into uart log// By default setting to FALSE to avoid impacting boot performanceverbose = <PM_FALSE>;driver-post-init = <// PM_CLK_ENABLE PM_BUSID_0 PMIC_A PM_CLK_RF_1 PM_TRUE.../*Delay*/PM_DELAY(10)> ;apply-rsns-trim = <PM_FALSE>;rsns-trim-value = <0>;};
再查看pm_sbl_boot_oem.c内是如何解析这个设备树内的节点信息的
static pm_err_flag_typepm_post_driver_init_dt_config( void ){pm_err_flag_type err_flag = PM_ERR_FLAG_SUCCESS;uint16 spmi_clk_data_cfg = 0;uint32 pmic_index = 0;uint32 periph_id = 0;uint32 value = 0;uint32 operation = 0;uint32 bus_id = 0;int i = 0;pm_model_type model = PMIC_IS_INVALID;pm_dt_sw_config *sw_dt_config = NULL;sw_dt_config = pm_dt_get_node( PMIC_DT_NODE_PM_SW_CONFIG );if((sw_dt_config != NULL) && (sw_dt_config->post_driver_init != NULL) && (sw_dt_config->post_driver_init_count > 0)){for(i = 0; i < sw_dt_config->post_driver_init_count; i++){operation = sw_dt_config->post_driver_init[i * 5];bus_id = sw_dt_config->post_driver_init[(i * 5) + 1];pmic_index = sw_dt_config->post_driver_init[(i * 5) + 2];periph_id = sw_dt_config->post_driver_init[(i * 5) + 3];value = sw_dt_config->post_driver_init[(i * 5) + 4];...switch( operation ){case PM_LDO_SET_ENABLE:err_flag |= pm_ldo_sw_enable(pmic_index, periph_id, value, TRUE);break;case PM_LDO_SET_VOLT:err_flag |= pm_ldo_volt_level(pmic_index, periph_id, value * 1000, TRUE); // *1000 to change to uvbreak;case PM_LDO_SET_MODE:err_flag |= pm_ldo_sw_mode(pmic_index, periph_id, value);break;...}}}}
解析设备树的时候，会根据post_driver_init内的5个属性进行解析，分别为operation、bus_id、pmic_index、periph_id、value。再跟一下代码，可以看到operation就是就是作为选择项去调用各个对应的api，对剩余的4个参数进行修改。再看看哪里定义了这些operation，从而找到我们想要使用的
//GPIO#define PM_GPIO_SET_ENABLE60#define PM_GPIO_SET_CFG_MODE 61#define PM_GPIO_SET_OUTPUT_LVL62#define PM_GPIO_SET_VOLT_SRC 63#define PM_GPIO_SET_OUT_BUFF_CONFIG 64#define PM_GPIO_SET_OUT_DRV_STR65#define PM_GPIO_SET_OUT_SRC_CFG66#define PM_GPIO_SET_PULL_SEL 67
根据我们的需求，我们需要先将这个gpio设置为IN模式，将这个gpio默认变为拉低状态，接收从mcu传来拉低的状态再去做我们的功能
那么我们的pm.dtsi内要如何设置也可以得出结论了：
sw-config {compatible = "qcom,pm-sw";// verbose: Set to TRUE will output verbose PON reason into uart log.//Set to 2 will output verbose PON reason and raw data into uart log// By default setting to FALSE to avoid impacting boot performanceverbose = <PM_FALSE>;driver-post-init = <// PM_CLK_ENABLE PM_BUSID_0 PMIC_A PM_CLK_RF_1 PM_TRUEPM_GPIO_SET_ENABLE PM_BUSID_0 PMIC_B PM_GPIO_06 TRUEPM_GPIO_SET_CFG_MODEPM_BUSID_0 PMIC_B PM_GPIO_06 TRUEPM_GPIO_SET_PULL_SELPM_BUSID_0 PMIC_B PM_GPIO_06 PM_GPIO_PULL_UP_30UA.../*Delay*/PM_DELAY(10)> ;apply-rsns-trim = <PM_FALSE>;rsns-trim-value = <0>;};
至此结束。编译后使用示波器进行量取对应的GPIO波形，修改之前为高电平，修改之后为低电平，并且abl内能判断逻辑也pass。
如有不对，麻烦大佬指点，谢谢
