通过对 NXP 维护 Linux4.1.15 源码进行分析。
一、确定驱动源码
思路：通过 imx6ull.dtsi 设备树文件，找到 UART 中 compatible 属性值，在驱动源码中查找相匹配驱动。
打开 imx6ull.dtsi 文件，找到UART3 对应的子节点，子节点内容如下所示：
uart3: serial@021ec000 {
compatible = "fsl,imx6ul-uart",
"fsl,imx6q-uart", "fsl,imx21-uart";
reg = <0x021ec000 0x4000>;
interrupts = <GIC_SPI 28 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6UL_CLK_UART3_IPG>,
<&clks IMX6UL_CLK_UART3_SERIAL>;
clock-names = "ipg", "per";
dmas = <&sdma 29 4 0>, <&sdma 30 4 0>;
dma-names = "rx", "tx";
status = "disabled";
};
compatible 属性，这里一共有三个值：“fsl,imx6ul-uart”、“fsl,imx6q-uar”和“fsl,imx21-uart”。在 linux 源码中搜索这三个值即可找到对应的UART 驱动文件，此文 件为 drivers/tty/serial/imx.c，在此文件中可以找到如下内容：
static const struct of_device_id imx_uart_dt_ids[] = {
{ .compatible = "fsl,imx6q-uart", .data = &imx_uart_devdata[IMX6Q_UART], },
{ .compatible = "fsl,imx1-uart", .data = &imx_uart_devdata[IMX1_UART], },
{ .compatible = "fsl,imx21-uart", .data = &imx_uart_devdata[IMX21_UART], },
{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, imx_uart_dt_ids);
通过以上信息可以确定，drivers/tty/serial/imx.c 文件为 I.MX6U 驱动源码。
二、驱动加载函数分析
static int __init imx_serial_init(void)
{
int ret = uart_register_driver(&imx_reg);
if (ret)
return ret;
ret = platform_driver_register(&serial_imx_driver);
if (ret != 0)
uart_unregister_driver(&imx_reg);
return ret;
}
imx_serial_init 函数功能：
1、调用 uart_register_driver 函数注册 imx_reg 串口驱动。
2、调用 platform_driver_register 函数注册 serial_imx_driver platform驱动。
三、imx_reg 初始化状态
四、serial_imx_driver 初始化状态
五、uart_register_driver(&imx_reg)分析
源码如下：
/**
* uart_register_driver - register a driver with the uart core layer 向uart核心层注册一个驱动程序
* @drv: low level driver structure 底层驱动结构
*
* Register a uart driver with the core driver. We in turn register
* with the tty layer, and initialise the core driver per-port state.
* 用核心驱动注册一个uart驱动。
* 我们依次向tty层注册，并初始化每个端口的核心驱动程序状态。
*
* We have a proc file in /proc/tty/driver which is named after the
* normal driver. 我们在 /proc/tty/driver 中有一个 proc 文件，它以普通驱动程序命名。
*
* drv->port should be NULL, and the per-port structures should be
* registered using uart_add_one_port after this call has succeeded.
* drv->port 应为 NULL，并且在此调用成功后，应使用 uart_add_one_port 注册每个端口的结构。
*/
int uart_register_driver(struct uart_driver *drv)
{
struct tty_driver *normal;
int i, retval;
BUG_ON(drv->state);
/*
* Maybe we should be using a slab cache for this, especially if
* we have a large number of ports to handle.
* 也许我们应该使用一个slab缓存，特别是当我们有大量的端口要处理的时候。
*/
drv->state = kzalloc(sizeof(struct uart_state) * drv->nr, GFP_KERNEL);
if (!drv->state)
goto out;
normal = alloc_tty_driver(drv->nr);
if (!normal)
goto out_kfree;
drv->tty_driver = normal;
normal->driver_name = drv->driver_name;
normal->name = drv->dev_name;
normal->major = drv->major;
normal->minor_start = drv->minor;
normal->type = TTY_DRIVER_TYPE_SERIAL;
normal->subtype = SERIAL_TYPE_NORMAL;
normal->init_termios = tty_std_termios;
normal->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
normal->init_termios.c_ispeed = normal->init_termios.c_ospeed = 9600;
normal->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
normal->driver_state = drv;
tty_set_operations(normal, &uart_ops);
/*
* Initialise the UART state(s).
*/
for (i = 0; i < drv->nr; i++) {
struct uart_state *state = drv->state + i;
struct tty_port *port = &state->port;
tty_port_init(port);
port->ops = &uart_port_ops;
}
retval = tty_register_driver(normal);
if (retval >= 0)
return retval;
for (i = 0; i < drv->nr; i++)
tty_port_destroy(&drv->state[i].port);
put_tty_driver(normal);
out_kfree:
kfree(drv->state);
out:
return -ENOMEM;
}
1、分析1
drv->state = kzalloc(sizeof(struct uart_state) * drv->nr, GFP_KERNEL);
if (!drv->state)
goto out;
drv：为 uart_register_driver 传入参数指针，也就是 imx_reg 变量首地址。
drv->state：就是 imx_reg.state。
drv->nr：就是 imx_reg.nr，此字段保存芯片 uart 个数。
以上代码主要作用是依照 uart 个数分配空间，并将首地址赋值给 imx_reg.state。
2、分析2
normal = alloc_tty_driver(drv->nr);
if (!normal)
goto out_kfree;
drv->tty_driver = normal;
normal->driver_name = drv->driver_name;
normal->name = drv->dev_name;
normal->major = drv->major;
normal->minor_start = drv->minor;
normal->type = TTY_DRIVER_TYPE_SERIAL;
normal->subtype = SERIAL_TYPE_NORMAL;
normal->init_termios = tty_std_termios;
normal->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
normal->init_termios.c_ispeed = normal->init_termios.c_ospeed = 9600;
normal->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
normal->driver_state = drv;
tty_set_operations(normal, &uart_ops);
void tty_set_operations(struct tty_driver *driver,
const struct tty_operations *op)
{
driver->ops = op;
};
static const struct tty_operations uart_ops = {
.open = uart_open,
.close = uart_close,
.write = uart_write,
.put_char = uart_put_char,
.flush_chars = uart_flush_chars,
.write_room = uart_write_room,
.chars_in_buffer= uart_chars_in_buffer,
.flush_buffer = uart_flush_buffer,
.ioctl = uart_ioctl,
.throttle = uart_throttle,
.unthrottle = uart_unthrottle,
.send_xchar = uart_send_xchar,
.set_termios = uart_set_termios,
.set_ldisc = uart_set_ldisc,
.stop = uart_stop,
.start = uart_start,
.hangup = uart_hangup,
.break_ctl = uart_break_ctl,
.wait_until_sent= uart_wait_until_sent,
#ifdef CONFIG_PROC_FS
.proc_fops = &uart_proc_fops,
#endif
.tiocmget = uart_tiocmget,
.tiocmset = uart_tiocmset,
.get_icount = uart_get_icount,
#ifdef CONFIG_CONSOLE_POLL
.poll_init = uart_poll_init,
.poll_get_char = uart_poll_get_char,
.poll_put_char = uart_poll_put_char,
#endif
};
drv->tty_driver：就是 imx_reg.tty_driver。
以上源码主要作用为，为 imx_reg.tty_driver 分配空间，并进行初始化。
3、分析3
/*
* Initialise the UART state(s).
*/
for (i = 0; i < drv->nr; i++) {
struct uart_state *state = drv->state + i;
struct tty_port *port = &state->port;
tty_port_init(port);
port->ops = &uart_port_ops;
}
static const struct tty_port_operations uart_port_ops = {
.activate = uart_port_activate,
.shutdown = uart_port_shutdown,
.carrier_raised = uart_carrier_raised,
.dtr_rts = uart_dtr_rts,
};
以上代码主要作用是为 imx_reg.state.port 赋值。
4、分析4
retval = tty_register_driver(normal);
if (retval >= 0)
return retval;
以上代码主要作用注册 tty_driver 驱动。
5、总结
uart_register_driver(&imx_reg) 主要作用如下：
1、初始化 imx_reg 变量。
2、注册 tty_driver 驱动。
六、platform_driver_register(&serial_imx_driver) 分析
platform_driver_register(&serial_imx_driver) 主要作用注册 platform 驱动，不进行详细分析。
七、serial_imx_probe 分析
当 UART 驱动和设备匹配成功以后，serial_imx_probe 函数将被执行。
static int serial_imx_probe(struct platform_device *pdev)
{
struct imx_port *sport;
void __iomem *base;
int ret = 0;
struct resource *res;
int txirq, rxirq, rtsirq;
sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
if (!sport)
return -ENOMEM;
ret = serial_imx_probe_dt(sport, pdev);
if (ret > 0)
serial_imx_probe_pdata(sport, pdev);
else if (ret < 0)
return ret;
// 从设备树中获取 I.MX 系列 SOC UART 外设寄存器首地址
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(base))
return PTR_ERR(base);
// 获取中断信息
rxirq = platform_get_irq(pdev, 0);
txirq = platform_get_irq(pdev, 1);
rtsirq = platform_get_irq(pdev, 2);
// 初始化 sport
sport->port.dev = &pdev->dev;
sport->port.mapbase = res->start;
sport->port.membase = base;
sport->port.type = PORT_IMX,
sport->port.iotype = UPIO_MEM;
sport->port.irq = rxirq;
sport->port.fifosize = 32;
sport->port.ops = &imx_pops; // imx_pops 就是 I.MX6ULL 最底层的驱动函数集合
sport->port.rs485_config = imx_rs485_config;
sport->port.rs485.flags =
SER_RS485_RTS_ON_SEND | SER_RS485_RX_DURING_TX;
sport->port.flags = UPF_BOOT_AUTOCONF;
init_timer(&sport->timer);
sport->timer.function = imx_timeout;
sport->timer.data = (unsigned long)sport;
sport->clk_ipg = devm_clk_get(&pdev->dev, "ipg");
if (IS_ERR(sport->clk_ipg)) {
ret = PTR_ERR(sport->clk_ipg);
dev_err(&pdev->dev, "failed to get ipg clk: %d\n", ret);
return ret;
}
sport->clk_per = devm_clk_get(&pdev->dev, "per");
if (IS_ERR(sport->clk_per)) {
ret = PTR_ERR(sport->clk_per);
dev_err(&pdev->dev, "failed to get per clk: %d\n", ret);
return ret;
}
sport->port.uartclk = clk_get_rate(sport->clk_per);
if (sport->port.uartclk > IMX_MODULE_MAX_CLK_RATE) {
ret = clk_set_rate(sport->clk_per, IMX_MODULE_MAX_CLK_RATE);
if (ret < 0) {
dev_err(&pdev->dev, "clk_set_rate() failed\n");
return ret;
}
}
sport->port.uartclk = clk_get_rate(sport->clk_per);
/*
* Allocate the IRQ(s) i.MX1 has three interrupts whereas later
* chips only have one interrupt.
*/
// 申请中断
if (txirq > 0) {
ret = devm_request_irq(&pdev->dev, rxirq, imx_rxint, 0,
dev_name(&pdev->dev), sport);
if (ret)
return ret;
ret = devm_request_irq(&pdev->dev, txirq, imx_txint, 0,
dev_name(&pdev->dev), sport);
if (ret)
return ret;
} else {
ret = devm_request_irq(&pdev->dev, rxirq, imx_int, 0,
dev_name(&pdev->dev), sport);
if (ret)
return ret;
}
imx_ports[sport->port.line] = sport;
platform_set_drvdata(pdev, sport);
// 向 uart_driver 添加 uart_port
return uart_add_one_port(&imx_reg, &sport->port);
}
static struct uart_ops imx_pops = {
.tx_empty = imx_tx_empty,
.set_mctrl = imx_set_mctrl,
.get_mctrl = imx_get_mctrl,
.stop_tx = imx_stop_tx,
.start_tx = imx_start_tx,
.stop_rx = imx_stop_rx,
.enable_ms = imx_enable_ms,
.break_ctl = imx_break_ctl,
.startup = imx_startup,
.shutdown = imx_shutdown,
.flush_buffer = imx_flush_buffer,
.set_termios = imx_set_termios,
.type = imx_type,
.config_port = imx_config_port,
.verify_port = imx_verify_port,
#if defined(CONFIG_CONSOLE_POLL)
.poll_init = imx_poll_init,
.poll_get_char = imx_poll_get_char,
.poll_put_char = imx_poll_put_char,
#endif
};
imx_pops 中的函数基本都是和 I.MX6ULL 的 UART 寄存器打交道的。
八、串口驱动使用
I.MX6U 的 UART 驱动 NXP 已经编写好了，所以不需要我们编写。
我们要做的就是在设备树中添加 UART3 对应的设备节点即可。
1、检查引脚是否使用
pinctrl_uart2: uart2grp {
fsl,pins = <
MX6UL_PAD_UART2_TX_DATA__UART2_DCE_TX 0x1b0b1
MX6UL_PAD_UART2_RX_DATA__UART2_DCE_RX 0x1b0b1
MX6UL_PAD_UART3_RX_DATA__UART2_DCE_RTS 0x1b0b1
MX6UL_PAD_UART3_TX_DATA__UART2_DCE_CTS 0x1b0b1
>;
};
通过查找设备树，pinctrl_uart2 中使用 UART3 引脚。因此，需要注释掉。
2、在设备树中添加引脚复用
pinctrl_uart3: uart3grp {
fsl,pins = <
MX6UL_PAD_UART3_TX_DATA__UART3_DCE_TX 0X1b0b1
MX6UL_PAD_UART3_RX_DATA__UART3_DCE_RX 0X1b0b1
>;
};
3、设备树中增加uart3节点
&uart3 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_uart3>;
status = "okay";
};
4、测试
添加前 Linux 启动日志如下：
编译设备树：
onlylove@ubuntu:~/linux/linux/lq_linux/linux-imx-rel_imx_4.1.15_2.1.0_ga$ make dtbs
CHK include/config/kernel.release
CHK include/generated/uapi/linux/version.h
CHK include/generated/utsrelease.h
make[1]: 'include/generated/mach-types.h' is up to date.
CHK include/generated/bounds.h
CHK include/generated/asm-offsets.h
CALL scripts/checksyscalls.sh
DTC arch/arm/boot/dts/imx6ull-lq-evk.dtb
onlylove@ubuntu:~/linux/linux/lq_linux/linux-imx-rel_imx_4.1.15_2.1.0_ga$
添加后 Linux 启动日志如下：
九、app程序
《待完成》