OpenRisc-20-or1200下linux的i2c(二)
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openrisc-3.1\drivers\i2c\busses\i2c-ocores.c,好~Open之,
然后回想一下之前blog里面写过的关于gpio字符驱动的内容,最后一步我们是把gpio的字符驱动封装成platform机制的,所以,照板煮碗,把代码拉到最后面就可以看到i2c-ocres.c也是同样的道理。
First,定义一个platform_driver结构。
Second,初始化这个结构,指定其probe、remove等函数,并初始化其中的driver变量。
Third,实现其probe、remove等函数。
以上是platform平台驱动的步骤。
然后说明一下i2c总线驱动负责的工作是:
First,申请i2c总线控制器所用到的硬件资源(IO、中断号、内存等等)。
Second,向内核增加一个i2c_adapter数据结构表示这个总线驱动,并且实现i2c_adapter数据结构中的algo成员(即控制i2c控制器的代码)。
所以总线驱动代码的综合效果就是将上面驱动负责的工作写入platform平台驱动,并注册完成i2c总线驱动。
下面来分析一下~
首先,例化关于i2c的平台驱动,这里编写的是对应i2c的总线驱动,所以在例化i2c总线驱动时的of_match_table列表要对应在DTS设备树文件中i2c的总线控制器的compatible,在module加载入kernel时才会按照名称搜索加载i2c的总线驱动。
DTS设备树i2c描述:
- i2c0: ocores@93000000 {
- compatible = "opencores,i2c-ocores";
- reg = <0x93000000 0x8>;
- interrupts = <5>;
- regstep = <1>;
- clock-frequency = <40000000>;
- #address-cells = <1>;
- #size-cells = <0>;
- eeprom@54 {
- compatible = "at24";
- reg = <0x54>;
- };
- };
总线驱动注册代码:
- static struct of_device_id ocores_i2c_match[] = {
- { .compatible = "opencores,i2c-ocores", },
- {},
- };
- MODULE_DEVICE_TABLE(of, ocores_i2c_match);
- /* work with hotplug and coldplug */
- MODULE_ALIAS("platform:ocores-i2c");
- static struct platform_driver ocores_i2c_driver = {
- .probe = ocores_i2c_probe,
- .remove = __devexit_p(ocores_i2c_remove),
- .suspend = ocores_i2c_suspend,
- .resume = ocores_i2c_resume,
- .driver = {
- .owner = THIS_MODULE,
- .name = "ocores-i2c",
- .of_match_table = ocores_i2c_match,
- },
- };
- static int __init ocores_i2c_init(void)
- {
- return platform_driver_register(&ocores_i2c_driver);
- }
- static void __exit ocores_i2c_exit(void)
- {
- platform_driver_unregister(&ocores_i2c_driver);
- }
- module_init(ocores_i2c_init);
- module_exit(ocores_i2c_exit);
然后,要实现probe、remove等函数
- static int __devinit ocores_i2c_probe(struct platform_device *pdev)
- {
- struct ocores_i2c *i2c;
- struct ocores_i2c_platform_data *pdata;
- struct resource *res, *res2;
- int ret;
- int i;
- //获取DTS文件中的IO资源(地址范围)
- res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
- if (!res)
- return -ENODEV;
- //获取DTS文件中的中断号资源
- res2 = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
- if (!res2)
- return -ENODEV;
- //申请内存
- i2c = devm_kzalloc(&pdev->dev, sizeof(*i2c), GFP_KERNEL);
- if (!i2c)
- return -ENOMEM;
- //检查是否有足够内存
- if (!devm_request_mem_region(&pdev->dev, res->start,
- resource_size(res), pdev->name)) {
- dev_err(&pdev->dev, "Memory region busy\n");
- return -EBUSY;
- }
- //i2c控制器wishbone总线物理地址映射到内核地址空间
- i2c->base = devm_ioremap_nocache(&pdev->dev, res->start,
- resource_size(res));
- if (!i2c->base) {
- dev_err(&pdev->dev, "Unable to map registers\n");
- return -EIO;
- }
- //例化一个指针指向platform_device的设备的私有数据域,这个数据从编译DTS文件时获取
- pdata = pdev->dev.platform_data;
- if (pdata) {
- i2c->regstep = pdata->regstep;
- i2c->clock_khz = pdata->clock_khz;
- } else {
- ret = ocores_i2c_of_probe(pdev, i2c);
- if (ret)
- return ret;
- }
- //初始化i2c控制器,具体可参考i2c_specs
- ocores_init(i2c);
- //初始化等待队列,目前我还没明白这个,水平有限
- init_waitqueue_head(&i2c->wait);
- //申请设备使用的中断号,并注册中断函数
- ret = devm_request_irq(&pdev->dev, res2->start, ocores_isr, 0,
- pdev->name, i2c);
- if (ret) {
- dev_err(&pdev->dev, "Cannot claim IRQ\n");
- return ret;
- }
- /* hook up driver to tree */
- //将i2c保存到platform_device中dev成员的p成员的driver_data数据域中
- platform_set_drvdata(pdev, i2c);
- i2c->adap = ocores_adapter;
- //将i2c保存到i2c_adapter中dev成员的p成员的driver_data数据域中
- i2c_set_adapdata(&i2c->adap, i2c);
- i2c->adap.dev.parent = &pdev->dev;
- i2c->adap.dev.of_node = pdev->dev.of_node;
- /* add i2c adapter to i2c tree */
- //增加i2c adapter的数据结构
- ret = i2c_add_adapter(&i2c->adap);
- if (ret) {
- dev_err(&pdev->dev, "Failed to add adapter\n");
- return ret;
- }
- /* add in known devices to the bus */
- //如果在DTS文件中有多个共享总线驱动的从设备便会枚举出来
- if (pdata) {
- for (i = 0; i < pdata->num_devices; i++)
- i2c_new_device(&i2c->adap, pdata->devices + i);
- }
- return 0;
- }
- static int __devexit ocores_i2c_remove(struct platform_device* pdev)
- {
- //将之前保存在platform_device中dev成员的p成员的driver_data数据域中的数据取出
- struct ocores_i2c *i2c = platform_get_drvdata(pdev);
- /* disable i2c logic */
- //无效i2c总线控制器
- oc_setreg(i2c, OCI2C_CONTROL, oc_getreg(i2c, OCI2C_CONTROL)
- & ~(OCI2C_CTRL_EN|OCI2C_CTRL_IEN));
- /* remove adapter & data */
- //删除完成注册的i2c_adapter
- i2c_del_adapter(&i2c->adap);
- //删除platform_device中dev成员的p成员的driver_data
- platform_set_drvdata(pdev, NULL);
- return 0;
- }
至于有关电源管理的suspend和resume暂且忽略,内核配置中暂时不去实现。
这样就注册好平台设备驱动。
接下去就在源码中去结合注释和i2c-specs的文档好好看看通信算法处理函数,这也是我们从新开发总线驱动的时候必须去编写的代码~
首先是定义i2c_adapter和其成员变量的algo算法
- static u32 ocores_func(struct i2c_adapter *adap)
- {
- return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
- }
- //定义一个i2c_algorithm的数据结构,其中实现控制器通信算法master_xfer
- //和functionality(master_xfer通信算法支持的协议)
- static const struct i2c_algorithm ocores_algorithm = {
- .master_xfer = ocores_xfer,
- .functionality = ocores_func,
- };
- //定义一个i2c_adapter,完成总线控制器的描述,并在probe中向内核注册
- static struct i2c_adapter ocores_adapter = {
- .owner = THIS_MODULE,
- .name = "i2c-ocores",
- .class = I2C_CLASS_HWMON | I2C_CLASS_SPD,
- .algo = &ocores_algorithm,
- };
其中由于这个驱动是基于中断架构的收发,结合源码继续往下看。
首先看看在probe中调用的ocores_init(),完成的是总线控制器的初始化
- //根据i2c-specs文档初始化总线控制器
- //对比文档中的寄存器进行操作
- static void ocores_init(struct ocores_i2c *i2c)
- {
- int prescale;
- //取出Control register寄存器的值,在i2c-specs中有说明~
- u8 ctrl = oc_getreg(i2c, OCI2C_CONTROL);
- /* make sure the device is disabled */
- //i2c cores禁止中断和无效总线控制器
- oc_setreg(i2c, OCI2C_CONTROL, ctrl & ~(OCI2C_CTRL_EN|OCI2C_CTRL_IEN));
- //设置i2c总线控制器的通信速率,在i2c-specs文档有计算公式
- prescale = (i2c->clock_khz / (5*100)) - 1;
- //将速率写入PRERlo和PRERhi寄存器
- oc_setreg(i2c, OCI2C_PRELOW, prescale & 0xff);
- oc_setreg(i2c, OCI2C_PREHIGH, prescale >> 8);
- /* Init the device */
- //清除中断标志位,使能总线控制器的中断和使能总线控制器
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_IACK);
- oc_setreg(i2c, OCI2C_CONTROL, ctrl | OCI2C_CTRL_IEN | OCI2C_CTRL_EN);
- }
然后程序调用通信算法时会hold住,在中断中处理数据,然后等待事件集到来,完成通信。
- //发送和接收调用的总线通信算法函数
- static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
- {
- //在ocores_i2c中有i2c_adapter成员,而i2c_adapter成员在probe进行时
- //已经由i2c_set_adapdata()保存到i2c_adapter中,所以这里取出保存在
- //i2c_adapter中dev成员的p成员的driver_data数据域
- struct ocores_i2c *i2c = i2c_get_adapdata(adap);
- //获取由应用层传入的i2c message
- i2c->msg = msgs;
- i2c->pos = 0;
- i2c->nmsgs = num;
- i2c->state = STATE_START;
- //根据i2c message类型是读还是写进行器件地址选择和设置LSB的读写位
- oc_setreg(i2c, OCI2C_DATA,
- (i2c->msg->addr << 1) |
- ((i2c->msg->flags & I2C_M_RD) ? 1:0));
- //根据i2c协议第一次是写器件地址和读写位的组合
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
- //等待事件集到来,???操作系统没学过,现在恶补
- if (wait_event_timeout(i2c->wait, (i2c->state == STATE_ERROR) ||
- (i2c->state == STATE_DONE), HZ))
- return (i2c->state == STATE_DONE) ? num : -EIO;
- else
- return -ETIMEDOUT;
- }
- //当总线控制器完成一个byte发送和接收时调用的中断函数
- //因为这个驱动采用了中断的方式收发数据
- static irqreturn_t ocores_isr(int irq, void *dev_id)
- {
- struct ocores_i2c *i2c = dev_id;
- ocores_process(i2c);
- return IRQ_HANDLED;
- }
- //中断处理函数的处理过程,目前没认真整理过,根据i2c通信协议再好好看看
- //然后有时间再总结出来
- static void ocores_process(struct ocores_i2c *i2c)
- {
- struct i2c_msg *msg = i2c->msg;
- u8 stat = oc_getreg(i2c, OCI2C_STATUS);
- if ((i2c->state == STATE_DONE) || (i2c->state == STATE_ERROR)) {
- /* stop has been sent */
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_IACK);
- wake_up(&i2c->wait);
- return;
- }
- /* error? */
- if (stat & OCI2C_STAT_ARBLOST) {
- i2c->state = STATE_ERROR;
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
- return;
- }
- if ((i2c->state == STATE_START) || (i2c->state == STATE_WRITE)) {
- i2c->state =
- (msg->flags & I2C_M_RD) ? STATE_READ : STATE_WRITE;
- if (stat & OCI2C_STAT_NACK) {
- i2c->state = STATE_ERROR;
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
- return;
- }
- } else
- msg->buf[i2c->pos++] = oc_getreg(i2c, OCI2C_DATA);
- /* end of msg? */
- if (i2c->pos == msg->len) {
- i2c->nmsgs--;
- i2c->msg++;
- i2c->pos = 0;
- msg = i2c->msg;
- if (i2c->nmsgs) { /* end? */
- /* send start? */
- if (!(msg->flags & I2C_M_NOSTART)) {
- u8 addr = (msg->addr << 1);
- if (msg->flags & I2C_M_RD)
- addr |= 1;
- i2c->state = STATE_START;
- oc_setreg(i2c, OCI2C_DATA, addr);
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
- return;
- } else
- i2c->state = (msg->flags & I2C_M_RD)
- ? STATE_READ : STATE_WRITE;
- } else {
- i2c->state = STATE_DONE;
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
- return;
- }
- }
- if (i2c->state == STATE_READ) {
- oc_setreg(i2c, OCI2C_CMD, i2c->pos == (msg->len-1) ?
- OCI2C_CMD_READ_NACK : OCI2C_CMD_READ_ACK);
- } else {
- oc_setreg(i2c, OCI2C_DATA, msg->buf[i2c->pos++]);
- oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_WRITE);
- }
- }
另外还有两个读写寄存器的函数,相信聪明你的绝对是看得明白的~不解释了~
- //这两个函数没什么好解释的了,大家都能看得懂的了
- //至于regstep在DTS文件中定义(寄存器的步长),对应的i2c-specs中寄存器步长为1
- static inline void oc_setreg(struct ocores_i2c *i2c, int reg, u8 value)
- {
- iowrite8(value, i2c->base + reg * i2c->regstep);
- }
- static inline u8 oc_getreg(struct ocores_i2c *i2c, int reg)
- {
- return ioread8(i2c->base + reg * i2c->regstep);
- }
先到这里了,至于文章中我觉得没说明白的地方在有时间的时候会补齐的~今天要把食梦者第3季给追完啦~谢谢各位捧场啦~
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