Linux驱动分析之Uart驱动
前言
之前对Uart驱动的整体架构做了介绍，现在来分析具体的驱动程序。我们以NXP 的 IMX6来进行分析。
Uart驱动分析
内核：4.20
芯片：NXP IMX6
下面的代码分析主要都在注释中，会按照驱动中函数的执行顺序分析。
(1) 装载和卸载函数
//dts匹配表
static const struct of_device_id imx_uart_dt_ids[] = {
{ .compatible = "fsl,imx6q-uart", .data = &imx_uart_devdata[IMX6Q_UART], },
{ .compatible = "fsl,imx53-uart", .data = &imx_uart_devdata[IMX53_UART], },
{ .compatible = "fsl,imx1-uart", .data = &imx_uart_devdata[IMX1_UART], },
{ .compatible = "fsl,imx21-uart", .data = &imx_uart_devdata[IMX21_UART], },
{ /* sentinel */ }
};
static struct uart_driver imx_uart_uart_driver = {
.owner = THIS_MODULE,
.driver_name = DRIVER_NAME,
.dev_name = DEV_NAME, //设备节点名
.major = SERIAL_IMX_MAJOR, //主设备号
.minor = MINOR_START, //次设备号
.nr = ARRAY_SIZE(imx_uart_ports), //串口数
.cons = IMX_CONSOLE,
};
static struct platform_driver imx_uart_platform_driver = {
.probe = imx_uart_probe, //driver和device匹配后回调
.remove = imx_uart_remove,
.id_table = imx_uart_devtype,
.driver = {
.name = "imx-uart",
.of_match_table = imx_uart_dt_ids,
.pm = &imx_uart_pm_ops,
},
};
//加载函数
static int __init imx_uart_init(void)
{
//注册uart_driver
int ret = uart_register_driver(&imx_uart_uart_driver);
//注册platform_driver
ret = platform_driver_register(&imx_uart_platform_driver);
return ret;
}
//卸载函数
static void __exit imx_uart_exit(void)
{
//注销uart_driver和platform_driver
platform_driver_unregister(&imx_uart_platform_driver);
uart_unregister_driver(&imx_uart_uart_driver);
}
module_init(imx_uart_init);
module_exit(imx_uart_exit);
上面真正回调probe的是匹配platform_driver, 而不是uart_driver。所以我们会看到调用了uart_register_driver 和 platform_driver_register 。
uart_register_driver是为了向uart核心层注册。
(2) probe()函数
static int imx_uart_probe(struct platform_device *pdev)
{
struct imx_port *sport; //nxp对uart_port进行了封装，添加自己的成员
void __iomem *base;
int ret = 0;
u32 ucr1;
struct resource *res;
int txirq, rxirq, rtsirq;
//分配内存，并清0
sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
if (!sport)
return -ENOMEM;
//解析设备树，保存到imx_port
ret = imx_uart_probe_dt(sport, pdev);
if (ret > 0)
imx_uart_probe_pdata(sport, pdev);
else if (ret < 0)
return ret;
//省略....
//获取IO资源，并映射
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
base = devm_ioremap_resource(&pdev->dev, res);
//省略....
//获取RX,TX,RTS中断号
rxirq = platform_get_irq(pdev, 0);
txirq = platform_get_irq(pdev, 1);
rtsirq = platform_get_irq(pdev, 2);
//填充imx_port结构体
sport->port.dev = &pdev->dev;
sport->port.mapbase = res->start; //映射地址
sport->port.membase = base; //物理地址
sport->port.type = PORT_IMX,
sport->port.iotype = UPIO_MEM;
sport->port.irq = rxirq; //接收中断
sport->port.fifosize = 32;
sport->port.ops = &imx_uart_pops; //串口操作函数
sport->port.rs485_config = imx_uart_rs485_config; //485配置
sport->port.flags = UPF_BOOT_AUTOCONF;
timer_setup(&sport->timer, imx_uart_timeout, 0); //设置定时器
sport->gpios = mctrl_gpio_init(&sport->port, 0);
if (IS_ERR(sport->gpios))
return PTR_ERR(sport->gpios);
//获取IPG时钟
sport->clk_ipg = devm_clk_get(&pdev->dev, "ipg");
//省略....
//获取PER时钟
sport->clk_per = devm_clk_get(&pdev->dev, "per");
//省略....
sport->port.uartclk = clk_get_rate(sport->clk_per);
//使能IPG时钟
ret = clk_prepare_enable(sport->clk_ipg);
//省略....
//读取寄存器值
sport->ucr1 = readl(sport->port.membase + UCR1);
sport->ucr2 = readl(sport->port.membase + UCR2);
sport->ucr3 = readl(sport->port.membase + UCR3);
sport->ucr4 = readl(sport->port.membase + UCR4);
sport->ufcr = readl(sport->port.membase + UFCR);
uart_get_rs485_mode(&pdev->dev, &sport->port.rs485);
//省略....
imx_uart_rs485_config(&sport->port, &sport->port.rs485);
//下面都是对寄存器的配置，可以查看datasheet
ucr1 = imx_uart_readl(sport, UCR1);
ucr1 &= ~(UCR1_ADEN | UCR1_TRDYEN | UCR1_IDEN | UCR1_RRDYEN |
UCR1_TXMPTYEN | UCR1_RTSDEN);
imx_uart_writel(sport, ucr1, UCR1);
if (!imx_uart_is_imx1(sport) && sport->dte_mode) {
u32 ufcr = imx_uart_readl(sport, UFCR);
if (!(ufcr & UFCR_DCEDTE))
imx_uart_writel(sport, ufcr | UFCR_DCEDTE, UFCR);
imx_uart_writel(sport,
IMX21_UCR3_RXDMUXSEL | UCR3_ADNIMP | UCR3_DSR,
UCR3);
} else {
u32 ucr3 = UCR3_DSR;
u32 ufcr = imx_uart_readl(sport, UFCR);
if (ufcr & UFCR_DCEDTE)
imx_uart_writel(sport, ufcr & ~UFCR_DCEDTE, UFCR);
if (!imx_uart_is_imx1(sport))
ucr3 |= IMX21_UCR3_RXDMUXSEL | UCR3_ADNIMP;
imx_uart_writel(sport, ucr3, UCR3);
}
clk_disable_unprepare(sport->clk_ipg);
//申请中断
if (txirq > 0) { //开启tx中断
ret = devm_request_irq(&pdev->dev, rxirq, imx_uart_rxint, 0,
dev_name(&pdev->dev), sport);
//省略.....
ret = devm_request_irq(&pdev->dev, txirq, imx_uart_txint, 0,
dev_name(&pdev->dev), sport);
//省略.....
ret = devm_request_irq(&pdev->dev, rtsirq, imx_uart_rtsint, 0,
dev_name(&pdev->dev), sport);
//省略.....
} else { //不开tx中断
ret = devm_request_irq(&pdev->dev, rxirq, imx_uart_int, 0,
dev_name(&pdev->dev), sport);
//省略.....
}
//保存imx_port
imx_uart_ports[sport->port.line] = sport;
platform_set_drvdata(pdev, sport);
//关联uart_driver和uart_port
return uart_add_one_port(&imx_uart_uart_driver, &sport->port);
}
上面其实主要是寄存器配置，中断申请，最后添加port。对裸机程序熟悉的，应该能很轻松的理解，因为我们不是为了针对某款芯片，所以寄存器配置可以忽略，主要还是为了理解Uart的驱动框架。
(3) 串口操作函数(uart_ops)
static const struct uart_ops imx_uart_pops = {
.tx_empty = imx_uart_tx_empty,
.set_mctrl = imx_uart_set_mctrl,
.get_mctrl = imx_uart_get_mctrl,
.stop_tx = imx_uart_stop_tx,
.start_tx = imx_uart_start_tx,
.stop_rx = imx_uart_stop_rx,
.enable_ms = imx_uart_enable_ms,
.break_ctl = imx_uart_break_ctl,
.startup = imx_uart_startup,
.shutdown = imx_uart_shutdown,
.flush_buffer = imx_uart_flush_buffer,
.set_termios = imx_uart_set_termios, //对串口进行配置
.type = imx_uart_type,
.config_port = imx_uart_config_port,
.verify_port = imx_uart_verify_port,
#if defined(CONFIG_CONSOLE_POLL)
.poll_init = imx_uart_poll_init,
.poll_get_char = imx_uart_poll_get_char,
.poll_put_char = imx_uart_poll_put_char,
#endif
};
上面的操作函数都是对具体芯片(IMX)的寄存器进行配置。需要根据具体的芯片手册来进行实现。我们简单看几个函数。
-
imx_uart_set_termios --- 配置串口
static void
imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
struct ktermios *old)
{
struct imx_port *sport = (struct imx_port *)port;
unsigned long flags;
u32 ucr2, old_ucr1, old_ucr2, ufcr;
unsigned int baud, quot;
unsigned int old_csize = old ? old->c_cflag & CSIZE : CS8;
unsigned long div;
unsigned long num, denom;
uint64_t tdiv64;
//设置数据位
while ((termios->c_cflag & CSIZE) != CS7 &&
(termios->c_cflag & CSIZE) != CS8) {
termios->c_cflag &= ~CSIZE;
termios->c_cflag |= old_csize;
old_csize = CS8;
}
if ((termios->c_cflag & CSIZE) == CS8)
ucr2 = UCR2_WS | UCR2_SRST | UCR2_IRTS;
else
ucr2 = UCR2_SRST | UCR2_IRTS;
//省略.....
//设置停止位
if (termios->c_cflag & CSTOPB)
ucr2 |= UCR2_STPB;
if (termios->c_cflag & PARENB) {
ucr2 |= UCR2_PREN;
if (termios->c_cflag & PARODD)
ucr2 |= UCR2_PROE;
}
del_timer_sync(&sport->timer);
//设置波特率
baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16);
quot = uart_get_divisor(port, baud);
spin_lock_irqsave(&sport->port.lock, flags);
//设置奇偶校验
sport->port.read_status_mask = 0;
if (termios->c_iflag & INPCK)
sport->port.read_status_mask |= (URXD_FRMERR | URXD_PRERR);
if (termios->c_iflag & (BRKINT | PARMRK))
sport->port.read_status_mask |= URXD_BRK;
//省略.....
//关闭中断
old_ucr1 = imx_uart_readl(sport, UCR1);
imx_uart_writel(sport,
old_ucr1 & ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN),
UCR1);
old_ucr2 = imx_uart_readl(sport, UCR2);
imx_uart_writel(sport, old_ucr2 & ~UCR2_ATEN, UCR2);
while (!(imx_uart_readl(sport, USR2) & USR2_TXDC))
barrier();
/* then, disable everything */
imx_uart_writel(sport, old_ucr2 & ~(UCR2_TXEN | UCR2_RXEN | UCR2_ATEN), UCR2);
old_ucr2 &= (UCR2_TXEN | UCR2_RXEN | UCR2_ATEN);
//计算波特率值
div = sport->port.uartclk / (baud * 16);
if (baud == 38400 && quot != div)
baud = sport->port.uartclk / (quot * 16);
div = sport->port.uartclk / (baud * 16);
if (div > 7)
div = 7;
if (!div)
div = 1;
rational_best_approximation(16 * div * baud, sport->port.uartclk,
1 << 16, 1 << 16, &num, &denom);
tdiv64 = sport->port.uartclk;
tdiv64 *= num;
do_div(tdiv64, denom * 16 * div);
tty_termios_encode_baud_rate(termios,
(speed_t)tdiv64, (speed_t)tdiv64);
num -= 1;
denom -= 1;
//对上面的设置写入到寄存器中
ufcr = imx_uart_readl(sport, UFCR);
ufcr = (ufcr & (~UFCR_RFDIV)) | UFCR_RFDIV_REG(div);
imx_uart_writel(sport, ufcr, UFCR);
imx_uart_writel(sport, num, UBIR);
imx_uart_writel(sport, denom, UBMR);
if (!imx_uart_is_imx1(sport))
imx_uart_writel(sport, sport->port.uartclk / div / 1000,
IMX21_ONEMS);
imx_uart_writel(sport, old_ucr1, UCR1);
/* set the parity, stop bits and data size */
imx_uart_writel(sport, ucr2 | old_ucr2, UCR2);
if (UART_ENABLE_MS(&sport->port, termios->c_cflag))
imx_uart_enable_ms(&sport->port);
spin_unlock_irqrestore(&sport->port.lock, flags);
}
应用层是通过struct termios来设置串口，传到底层就是struct ktermios。通过解析设置参数，然后配置对应的寄存器。
-
imx_uart_start_tx --- 串口发送
static void imx_uart_start_tx(struct uart_port *port)
{
struct imx_port *sport = (struct imx_port *)port;
u32 ucr1;
//判断是否有高优先级数据和环形buffer是否有数据
if (!sport->port.x_char && uart_circ_empty(&port->state->xmit))
return;
//省略......
//没有开启DMA，则使用Tx中断
if (!sport->dma_is_enabled) {
//触发Tx中断
ucr1 = imx_uart_readl(sport, UCR1);
imx_uart_writel(sport, ucr1 | UCR1_TXMPTYEN, UCR1);
}
if (sport->dma_is_enabled) {
if (sport->port.x_char) {
//有高优先级的数据要发送，则使用Tx中断，关闭DMA
ucr1 = imx_uart_readl(sport, UCR1);
ucr1 &= ~UCR1_TXDMAEN;
ucr1 |= UCR1_TXMPTYEN;
imx_uart_writel(sport, ucr1, UCR1);
return;
}
//环形buffer有数据，并且串口没有停止，则使用DMA进行发送
if (!uart_circ_empty(&port->state->xmit) &&
!uart_tx_stopped(port))
imx_uart_dma_tx(sport); //DMA发送
return;
}
}
使用Tx中断进行发送或DMA进行发送。
-
imx_uart_rxint --- Rx中断处理函数
static irqreturn_t imx_uart_rxint(int irq, void *dev_id)
{
struct imx_port *sport = dev_id;
unsigned int rx, flg, ignored = 0;
struct tty_port *port = &sport->port.state->port;
spin_lock(&sport->port.lock);
while (imx_uart_readl(sport, USR2) & USR2_RDR) {
u32 usr2;
flg = TTY_NORMAL;
sport->port.icount.rx++;
rx = imx_uart_readl(sport, URXD0);
usr2 = imx_uart_readl(sport, USR2);
if (usr2 & USR2_BRCD) {
imx_uart_writel(sport, USR2_BRCD, USR2);
if (uart_handle_break(&sport->port))
continue;
}
//省略......
if (sport->port.ignore_status_mask & URXD_DUMMY_READ)
goto out;
//添加到tty核心层
if (tty_insert_flip_char(port, rx, flg) == 0)
sport->port.icount.buf_overrun++;
}
out:
spin_unlock(&sport->port.lock);
tty_flip_buffer_push(port); //push给tty核心层
return IRQ_HANDLED;
}
接收中断就是将收到的数据发送给tty核心层，让它去进行缓存。
总结
上面芯片相关的可以跳着看，我们主要是去看Uart驱动的套路。学习驱动就是在学习套路，掌握了套路，它们就会变成模板了。可以和之前的《Linux驱动分析之Uart驱动架构》一起看。
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