imx.536(cotex-a8核)的CAN驱动懂得一（probe）
imx.536(cotex-a8核)的CAN驱动理解一（probe）
下面看看这个函数的代码，看它们都干了什么？
//理解imx536的can驱动还是从probe开始吧，2.6版本内核can驱动是归属于网络驱动
//所以我得先去把网络驱动几个重要结构体先找出来吧。前进吧!年轻人。
static struct platform_driver flexcan_driver = {
.driver = {
.name = FLEXCAN_DEVICE_NAME,
},
.probe = flexcan_probe,
.remove = flexcan_remove,
.suspend = flexcan_suspend,
.resume = flexcan_resume,
};
下面看probe
static int flexcan_probe(struct platform_device *pdev)
{
//还是熟悉的struct net_device
struct net_device *net;
//这个函数估计得干大把大把的事吧，什么申请内存，什么初始化struct net_device及网络设备私有数据等
net = flexcan_device_alloc(pdev, flexcan_setup);
if (!net)
return -ENOMEM;
//注册网络设备
if (register_netdev(net)) {
flexcan_device_free(pdev);
return -ENODEV;
}
return 0;
}probe中主要是调用了flexcan_device_alloc，继续看flexcan_device_alloc
struct net_device *flexcan_device_alloc(struct platform_device *pdev,
void (*setup) (struct net_device *dev))
{
//can私有数据结构体
struct flexcan_device *flexcan;
struct net_device *net;
int i, num;
//申请内存，初始化net
net = alloc_netdev(sizeof(*flexcan), "can%d", setup);
if (net == NULL) {
printk(KERN_ERR "Allocate netdevice for FlexCAN fail!\n");
return NULL;
}
//flexcan指向net尾端，即私有数据结构体起始地址
flexcan = netdev_priv(net);
memset(flexcan, 0, sizeof(*flexcan));
//互斥锁初始化
mutex_init(&flexcan->mutex);
//初始化内核定时器
init_timer(&flexcan->timer);
flexcan->dev = pdev;
//注册中断,映射虚拟内存
if (flexcan_device_attach(flexcan)) {
printk(KERN_ERR "Attach FlexCAN fail!\n");
free_netdev(net);
return NULL;
}
//把板级配置文件中设置的struct flexcan_platform_data中的值，传递给flexcan
flexcan_device_default(flexcan);
//根据can的波特率去算br_presdiv,br_propseg,br_pseg1,br_pseg2这些变量的值
//因为flexcan->bitrate值未确定，所以在我的板上，这个函数不起效果
flexcan_set_bitrate(flexcan, flexcan->bitrate);
//重新计算波特率，保存在flexcan
flexcan_update_bitrate(flexcan);
//ARRAY_SIZE作用是取数组元素个数
num = ARRAY_SIZE(flexcan_dev_attr);
//device_create_file，添加属性文件，我的理解最终会设置文件系统sys目录下一些设备属性文件
//这些设备文件是在调用device_create时生成的。device_create这个函数什么时候调用的呢，这个就需要udev
//udev是什么?udev是设备管理器，能自动生成设备节点。
//在dm9000驱动里不知道为什么没看到这个函数?
for (i = 0; i < num; i++) {
if (device_create_file(&pdev->dev, flexcan_dev_attr + i)) {
printk(KERN_ERR "Create attribute file fail!\n");
break;
}
}
//上面操作的反向操作
if (i != num) {
for (; i >= 0; i--)
device_remove_file(&pdev->dev, flexcan_dev_attr + i);
free_netdev(net);
return NULL;
}
//保存net为设备私有数据
dev_set_drvdata(&pdev->dev, net);
return net;
}flexcan_device_alloc中最重要的几个函数flexcan_device_attach，flexcan_device_default，flexcan_set_bitratef，lexcan_update_bitrate下面看看这个函数的代码，看它们都干了什么？
static void flexcan_set_bitrate(struct flexcan_device *flexcan, int bitrate)
{
/* TODO:: implement in future
* based on the bitrate to get the timing of
* presdiv, pseg1, pseg2, propseg
*/
int i, rate, div;
bool found = false;
struct time_segment *segment;
rate = clk_get_rate(flexcan->clk);
if (!bitrate)
bitrate = DEFAULT_BITRATE;
//如果时钟正好是波特率的整数倍
if (rate % bitrate == 0)
{
//根据时钟是波特率的倍数去推算br_presdiv,br_propseg,br_pseg1,br_pseg2
div = rate / bitrate;
for (i = TIME_SEGMENT_MID; i <= TIME_SEGMENT_MAX; i++)
{
if (div % i == 0) {
found = true;
break;
}
}
if (!found) {
for (i = TIME_SEGMENT_MID - 1;
i >= TIME_SEGMENT_MIN; i--) {
if (div % i == 0) {
found = true;
break;
}
}
}
}
if (found) {
//time_segments数组中列出了各种br_presdiv,br_propseg,br_pseg1,br_pseg2组合值
//根据以上推算，确定i值，从而确定br_presdiv,br_propseg,br_pseg1,br_pseg2的值
segment = &time_segments[i - TIME_SEGMENT_MIN];
flexcan->br_presdiv = div/i - 1;
flexcan->br_propseg = segment->propseg;
flexcan->br_pseg1 = segment->pseg1;
flexcan->br_pseg2 = segment->pseg2;
flexcan->bitrate = bitrate;
} else {
pr_info("The bitrate %d can't supported with clock \
rate of %d \n", bitrate, rate);
}
}
static void flexcan_update_bitrate(struct flexcan_device *flexcan)
{
int rate, div;
//板级配置文件中设置的
struct flexcan_platform_data *plat_data;
plat_data = flexcan->dev->dev.platform_data;
//如果板级配置文件中，struct flexcan_platform_data中root_clk_id配置了
if (plat_data->root_clk_id)
rate = clk_get_rate(flexcan->clk);
else
{
//若struct flexcan_platform_data中root_clk_id未被配置，再看br_clksrc是否被配置成1
if (flexcan->br_clksrc)
rate = clk_get_rate(flexcan->clk);
//在我的imx536项目中，以上两个变量都未被配置，所以会执行以下代码
else
{
struct clk *clk;
clk = clk_get(NULL, "ckih");
if (!clk)
return;
//获取can时钟频率
rate = clk_get_rate(clk);
clk_put(clk);
}
}
if (!rate)
return;
//计算can传输速率
//其中br_presdiv,br_propseg,br_pseg1,br_pseg2,这些参数都是在板级配置文件中设置的
//所以可以实现由用户自己配置CAN波特率
div = (flexcan->br_presdiv + 1);
div *=
(flexcan->br_propseg + flexcan->br_pseg1 + flexcan->br_pseg2 + 4);
flexcan->bitrate = (rate + div - 1) / div;
}
static int flexcan_device_attach(struct flexcan_device *flexcan)
{
int ret;
struct resource *res;
struct platform_device *pdev = flexcan->dev;
struct flexcan_platform_data *plat_data = (pdev->dev).platform_data;
struct clk *can_root_clk;
//看到了熟悉的身影了
res = platform_get_resource(flexcan->dev, IORESOURCE_MEM, 0);
if (!res)
return -ENODEV;
//内存映射
flexcan->io_base = ioremap(res->start, res->end - res->start + 1);
if (!flexcan->io_base)
return -ENOMEM;
//咋没直接注册中断?
flexcan->irq = platform_get_irq(flexcan->dev, 0);
if (!flexcan->irq) {
ret = -ENODEV;
goto no_irq_err;
}
ret = -EINVAL;
if (plat_data) {
if (plat_data->core_reg) {
flexcan->core_reg = regulator_get(&pdev->dev,
plat_data->core_reg);
if (!flexcan->core_reg)
goto plat_err;
}
if (plat_data->io_reg) {
flexcan->io_reg = regulator_get(&pdev->dev,
plat_data->io_reg);
if (!flexcan->io_reg)
goto plat_err;
}
}
flexcan->clk = clk_get(&(flexcan->dev)->dev, "can_clk");
//如果板级配置文件中root_clk_id被配置了，can时钟源变成了root_clk_id
if (plat_data->root_clk_id)
{
can_root_clk = clk_get(NULL, plat_data->root_clk_id);
clk_set_parent(flexcan->clk, can_root_clk);
}
flexcan->hwmb = (struct can_hw_mb *)(flexcan->io_base + CAN_MB_BASE);
flexcan->rx_mask = (unsigned int *)(flexcan->io_base + CAN_RXMASK_BASE);
return 0;
//以后得多学学内核纠错处理了
plat_err:
if (flexcan->core_reg) {
regulator_put(flexcan->core_reg);
flexcan->core_reg = NULL;
}
no_irq_err:
if (flexcan->io_base)
iounmap(flexcan->io_base);
return ret;
}