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Blog: https://blog.csdn.net/fulinus
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概述

我们鸿蒙3.2设备上连接了sensor，如accel和gyro，是通过i2c总线连接的，在鸿蒙HDF的设备私有信息配置文件如下描述：

vendor/sprd/uis7885/hdf_config/khdf/sensor/accel/qmi8658_config.hcs
sensorBusConfig :: sensorBusInfo {busType = 0; // 0:i2c 1:spibusNum = 2;busAddr = 0x6b;regWidth = 1; // 1byte
}
sensorIdAttr :: sensorIdInfo {chipName = "qmi8658";chipIdRegister = 0x00;chipIdValue = 0x05;
}

即总线是i2c2，从设备的sensor地址是0x6b，chip id的寄存器地址是0x00。chip id值是0x5。
我们先研究下如何通过测试程序来操作I2C，读取这个chip id值。

I2C平台驱动

鸿蒙标准系统中，使用的是Linux内核，这个没有官网上的I2C平台驱动中描述的这样需要编写I2C平台驱动。
使用这个I2C平台驱动文件：drivers/hdf_core/adapter/khdf/linux/platform/i2c/i2c_adapter.c
比如获取对应的I2C adapter：

static int LinuxI2cProbe(struct device *dev, void *data)
{int32_t ret;struct I2cCntlr *cntlr = NULL;struct i2c_adapter *adapter = NULL;(void)data;if (dev == NULL) {HDF_LOGE("%s: dev is null", __func__);return HDF_ERR_INVALID_OBJECT;}   if (dev->type != &i2c_adapter_type) {return HDF_SUCCESS; // continue probe}   HDF_LOGI("%s: Enter", __func__);adapter = to_i2c_adapter(dev); //获取i2c adaptercntlr = (struct I2cCntlr *)OsalMemCalloc(sizeof(*cntlr));if (cntlr == NULL) {HDF_LOGE("%s: malloc cntlr fail!", __func__);i2c_put_adapter(adapter);return HDF_ERR_MALLOC_FAIL;}   cntlr->busId = adapter->nr;cntlr->priv = adapter;cntlr->ops = &g_method;ret = I2cCntlrAdd(cntlr); //这个I2C控制器添加到HDF框架中，后面会在I2cOpen函数中调用I2cCntlrGet函数查找到对应的控制器if (ret != HDF_SUCCESS) {i2c_put_adapter(adapter);OsalMemFree(cntlr);cntlr = NULL;HDF_LOGE("%s: add controller fail:%d", __func__, ret);return ret;}   HDF_LOGI("%s: i2c adapter %d add success", __func__, cntlr->busId);return HDF_SUCCESS;
}

参考：http://docs.openharmony.cn/pages/v3.2/zh-cn/device-dev/guide/device-driver-demo.md/
上面我们提及to_i2c_adapter添加i2c 适配器，然后又将总线ID、适配器和操作方法等通过I2cCntlrAdd添加到HDF驱动框架中，后面在UHDF或KHDF中通过调用I2cOpen函数，间接调用了I2cCntlrGet函数，在HDF框架中找到对应的总线ID、适配器和操作方法等，然后就可以操作I2C总线了。
I2cCntlrAdd函数：

//drivers/hdf_core/framework/support/platform/src/i2c/i2c_core.c
int32_t I2cCntlrAdd(struct I2cCntlr *cntlr)
{int32_t ret;if (cntlr == NULL) {return HDF_ERR_INVALID_OBJECT;}   if (cntlr->ops == NULL) {HDF_LOGE("I2cCntlrAdd: no ops supplied!");return HDF_ERR_INVALID_OBJECT;}   if (cntlr->lockOps == NULL) {HDF_LOGI("I2cCntlrAdd: use default lock methods!");cntlr->lockOps = &g_i2cLockOpsDefault;}   if (OsalMutexInit(&cntlr->lock) != HDF_SUCCESS) {HDF_LOGE("I2cCntlrAdd: init lock fail!");return HDF_FAILURE;}   ret = I2cManagerAddCntlr(cntlr);if (ret != HDF_SUCCESS) {(void)OsalMutexDestroy(&cntlr->lock);return ret;}   return HDF_SUCCESS;
}

I2cOpen函数：

DevHandle I2cOpen(int16_t number)
{return (DevHandle)I2cCntlrGet(number);
}

I2cCntlrGet函数：

/** Find an i2c controller by bus number, without ref count*/
static struct I2cCntlr *I2cManagerFindCntlr(int16_t number)
{struct I2cCntlr *cntlr = NULL;struct I2cManager *manager = g_i2cManager;if (number < 0 || number >= I2C_BUS_MAX) {HDF_LOGE("I2cManagerFindCntlr: invalid busId:%hd!", number);return NULL;}if (manager == NULL) {HDF_LOGE("I2cManagerFindCntlr: get i2c manager fail!");return NULL;}if (OsalMutexLock(&manager->lock) != HDF_SUCCESS) {HDF_LOGE("I2cManagerFindCntlr: lock i2c manager fail!");return NULL;}cntlr = manager->cntlrs[number];(void)OsalMutexUnlock(&manager->lock);return cntlr;
}/** Find and return an i2c controller by number, with ref count*/
struct I2cCntlr *I2cCntlrGet(int16_t number)
{return I2cManagerFindCntlr(number);
}

在drivers/hdf_core/framework/support/platform/src/i2c/i2c_core.c文件中，主要就是实现这个上述这些功能

I2C平台驱动HDF框架

I2C平台驱动既可以为其他HDF驱动提供接口，比如挂接在I2C总线上的sensor驱动，也可以为用户空间提供通用的操作接口。这些接口都是这些：I2cOpen()，I2cClose()，I2cTransfer()。所以可以在drivers/hdf_core/framework/support/platform/src/i2c/中看到有这两个文件：

drivers/hdf_core/framework/support/platform/src/i2c/i2c_if.c
drivers/hdf_core/framework/support/platform/src/i2c/i2c_if_u.c

其中i2c_if.c就是对其他HDF驱动提供接口的：

#include "i2c_if.h"
#include "devsvc_manager_clnt.h"
#include "hdf_base.h"
#include "hdf_log.h"
#include "i2c_core.h"
#include "osal_mem.h"
#include "securec.h"#define HDF_LOG_TAG i2c_if#define I2C_SERVICE_NAME "HDF_PLATFORM_I2C_MANAGER"DevHandle I2cOpen(int16_t number)
{return (DevHandle)I2cCntlrGet(number);
}void I2cClose(DevHandle handle)
{if (handle != NULL) {I2cCntlrPut((struct I2cCntlr *)handle);}
}int32_t I2cTransfer(DevHandle handle, struct I2cMsg *msgs, int16_t count)
{if (handle == NULL) {return HDF_ERR_INVALID_OBJECT;}if (msgs == NULL || count <= 0) {HDF_LOGE("I2cTransfer: err params! msgs:%s, count:%hd",(msgs == NULL) ? "0" : "x", count);return HDF_ERR_INVALID_PARAM;}return I2cCntlrTransfer((struct I2cCntlr *)handle, msgs, count);
}

其中i2c_if_u.c就是对用户空间提供通用的操作接口：

#include "hdf_base.h"
#include "hdf_io_service_if.h"
#include "hdf_log.h"
#include "i2c_if.h"
#include "i2c_service.h"