Linux驱动分析之Uart驱动-阿里云开发者社区

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staticconststructof_device_idimx_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 */ }
};
staticstructuart_driverimx_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,
};
staticstructplatform_driverimx_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staticint__initimx_uart_init(void)
{
//注册uart_driverintret=uart_register_driver(&imx_uart_uart_driver);
//注册platform_driverret=platform_driver_register(&imx_uart_platform_driver);
returnret;
}
//卸载函数staticvoid__exitimx_uart_exit(void)
{
//注销uart_driver和platform_driverplatform_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

staticintimx_uart_probe(structplatform_device*pdev)
{
structimx_port*sport; //nxp对uart_port进行了封装，添加自己的成员void__iomem*base;
intret=0;
u32ucr1;
structresource*res;
inttxirq, rxirq, rtsirq;
//分配内存，并清0sport=devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
if (!sport)
return-ENOMEM;
//解析设备树，保存到imx_portret=imx_uart_probe_dt(sport, pdev);
if (ret>0)
imx_uart_probe_pdata(sport, pdev);
elseif (ret<0)
returnret;
//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))
returnPTR_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datasheetucr1=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) {
u32ufcr=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 {
u32ucr3=UCR3_DSR;
u32ufcr=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_portimx_uart_ports[sport->port.line] =sport;
platform_set_drvdata(pdev, sport);
//关联uart_driver和uart_portreturnuart_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)

staticconststructuart_opsimx_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

staticvoidimx_uart_set_termios(structuart_port*port, structktermios*termios,
structktermios*old)
{
structimx_port*sport= (structimx_port*)port;
unsignedlongflags;
u32ucr2, old_ucr1, old_ucr2, ufcr;
unsignedintbaud, quot;
unsignedintold_csize=old?old->c_cflag&CSIZE : CS8;
unsignedlongdiv;
unsignedlongnum, denom;
uint64_ttdiv64;
//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;
elseucr2=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

staticvoidimx_uart_start_tx(structuart_port*port)
{
structimx_port*sport= (structimx_port*)port;
u32ucr1;
//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DMAucr1=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

staticirqreturn_timx_uart_rxint(intirq, void*dev_id)
{
structimx_port*sport=dev_id;
unsignedintrx, flg, ignored=0;
structtty_port*port=&sport->port.state->port;
spin_lock(&sport->port.lock);
while (imx_uart_readl(sport, USR2) &USR2_RDR) {
u32usr2;
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)
gotoout;
//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returnIRQ_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。

Linux驱动分析之Uart驱动

前言

Uart驱动分析

总结

热门文章

最新文章

相关课程

相关电子书

相关实验场景

推荐镜像

热门

活动广场

任务中心

开发者评测

高校计划

乘风者计划

训练营

阿里云MVP

话题

直播

下载

镜像站

技术资料

插件

Linux驱动分析之Uart驱动

前言

Uart驱动分析

总结

热门文章

最新文章

相关课程

相关电子书

相关实验场景

推荐镜像