Platform Driver (1)

Linux kernel中大部分设备可以归结为平台设备，因此大部分的驱动是平台驱动（patform driver）

什么是平台设备

平台设备是linux的设备模型中一类设备的抽象。 内核中的描述：

Platform devices are devices that typically appear as autonomous entities in the system. This includes legacy port-based devices and host bridges to peripheral buses, and most controllers integrated into system-on-chip platforms. What they usually have in common is direct addressing from a CPU bus. Rarely, a platform_device will be connected through a segment of some other kind of bus; but its registers will still be directly addressable.

一句话来描述就是： CPU能够直接寻址的SOC上的外设

图1：Platform设备

图1中的uart控制器，I2C控制器，GPIO控制器等，都是平台设备。

可以说，paltform设备对Linux驱动工程师是非常重要的，因为我们编写的大多数设备驱动，都是为了驱动plaftom设备。

Platform设备在内核中的实现主要包括三个部分：

• Platform Bus，基于底层bus模块，抽象出一个虚拟的Platform bus，用于挂载Platform设备；
• Platform Device，基于底层device模块，抽象出Platform Device，用于表示Platform设备；
• Platform Driver，基于底层device_driver模块，抽象出Platform Driver，用于驱动Platform设备

对于图1中的I2C控制器挂载在platform Bus上，因此我们在linux kernel中常说的I2C driver，都是指I2C controller driver，都是以platform driver的形式存在，当然，对应的控制器是platform device。

与此同时，kernel抽象出I2C bus（/sys/bus/i2c），用于挂载和I2C controller通过I2C总线连接的各个I2C slave device。

串口驱动开发

驱动开发框架

得益于设备模型，Linux kernel平台驱动的开发有了一套非常固定的框架

1）模块的入口和出口
用于注册/注销platform driver，这一部分的代码基本固定，包括函数和变量的命名方式也可固定，如下：

 /* 驱动模块加载 */static int __init xxxdriver_init(void){return platform_driver_register(&xxx_driver);}/* 驱动模块卸载 */static void __exit xxxdriver_exit(void){platform_driver_unregister(&xxx_driver);}module_init(xxxdriver_init);module_exit(xxxdriver_exit);MODULE_LICENSE("GPL V2");MODULE_AUTHOR("QianRuShi-ABC");

2）platform driver

基本的platform driver包含三要素：struct platform_driver变量、probe/remove函数、用于和device tree匹配的match table，如下：

/** platform 平台驱动结构体*/
static struct platform_driver xxx_driver = {.driver = {.name = "xxx",.of_match_table = xxx_of_match,},.probe = xxx_probe,.remove = xxx_remove,
};/** platform 驱动的 probe 函数* 驱动与设备匹配成功以后此函数就会执行*/static int xxx_probe(struct platform_device *dev){match = of_match_device(xxx_of_match, &pdev->dev);if (!match) {dev_err(&pdev->dev, "Error: No device match found\n");return -ENODEV;}return 0;}static int xxx_remove(struct platform_device *dev){....../* 函数具体内容 */return 0;}/* 匹配列表 */static const struct of_device_id xxx_of_match[] = {{ .compatible = "xxx-xxx" },{ /* Sentinel */ }};

注意，xxx_of_match中的.compatible需要和DTS文件中的compatible对应，一般格式是“厂商名称,芯片系列-模块名”，例如“actions,s900-serial”

##串口驱动
串口设备（serial or uart，后面不再区分）是TTY设备的一种，Linux kernel为了方便串口驱动的开发，在TTY framework的基础上，封装了一层串口框架（serial framework）。该框架尽可能的屏蔽了TTY有关的技术细节（比较难懂），驱动工程师在编写串口驱动的时候，只需要把精力放在串口以及串口控制器本身即可。

Linux kernel serial framework位于“drivers/tty/serial”目录中，其软件架构（如下面图2所示）比较简单：

图2： serialFramework

Serial core是Serial framework的核心实现，对上封装、屏蔽TTY的技术细节，对下为具体的串口驱动提供简单、统一的编程API。
Serial drivers就是具体的串口驱动。

Serial Core

serial core主要实现如下三类功能
1）将串口设备有关的物理对象（及其操作方法）封装成一个一个的数据结构，以达到用软件语言描述硬件的目的。

2）向底层driver提供串口驱动的编程接口。

3）基于TTY framework所提供的TTY driver的编写规则，将底层driver看到的serial driver，转换为TTY driver，并将所有的serial操作，转换为对应的tty操作。

关键数据结构

struct uart_port
struct uart_state
struct uart_ops
struct uart_driver

API:

int uart_register_driver(struct uart_driver *uart);
void uart_unregister_driver(struct uart_driver *uart);int uart_add_one_port(struct uart_driver *reg, struct uart_port *port);
int uart_remove_one_port(struct uart_driver *reg, struct uart_port *port);
int uart_match_port(struct uart_port *port1, struct uart_port *port2);int uart_suspend_port(struct uart_driver *reg, struct uart_port *port);
int uart_resume_port(struct uart_driver *reg, struct uart_port *port);static inline int uart_tx_stopped(struct uart_port *port)extern void uart_insert_char(struct uart_port *port, unsigned int status,unsigned int overrun, unsigned int ch, unsigned int flag);

串口驱动的移植步骤

• 定义并注册uart driver
• 注册uart port
• 定义并实现uart ops

定义并注册uart driver

static struct uart_driver imx_reg = {.owner          = THIS_MODULE,.driver_name    = DRIVER_NAME,.dev_name       = DEV_NAME,.major          = SERIAL_IMX_MAJOR,.minor          = MINOR_START,.nr             = ARRAY_SIZE(imx_ports),.cons           = IMX_CONSOLE,
};

注册uart port

platform device代表uart控制器，是实体抽象。对应的，uart port代表“串口”. 因此，我们需要在platform device probe的时候（platform driver的probe接口），动态分配并注册一个uart port（struct uart_port）。在后续的串口操作中，都是以uart port指针为对象. 见下一章节代码中i.mx6的驱动代码。

定义并实现uart ops

struct uart_ops结构包含了各式各样的uart端口的操作函数，需要在添加uart port的时候提供.见下一章节代码中i.mx6的驱动代码

完整代码

对应驱动开发框架中，1）模块的入口和出口

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;
}static void __exit imx_serial_exit(void)
{platform_driver_unregister(&serial_imx_driver);uart_unregister_driver(&imx_reg);
}module_init(imx_serial_init);
module_exit(imx_serial_exit);MODULE_AUTHOR("Sascha Hauer");
MODULE_DESCRIPTION("IMX generic serial port driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:imx-uart");

对应驱动开发框架中，2）platform driver

基本的platform driver包含三要素：struct platform_driver变量、probe/remove函数、用于和device tree匹配的match table

• struct platform_driver变量

static struct platform_driver serial_imx_driver = {.probe		= serial_imx_probe,.remove		= serial_imx_remove,.suspend	= serial_imx_suspend,.resume		= serial_imx_resume,.id_table	= imx_uart_devtype,.driver		= {.name	= "imx-uart",.of_match_table = imx_uart_dt_ids,},
};

• robe/remove函数

serial_imx_probe

 
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;
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(base))return PTR_ERR(base);rxirq = platform_get_irq(pdev, 0);
txirq = platform_get_irq(pdev, 1);
rtsirq = platform_get_irq(pdev, 2);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;
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.*/
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);
return uart_add_one_port(&imx_reg, &sport->port);

}

serial_imx_remove

static int serial_imx_remove(struct platform_device *pdev)
{struct imx_port *sport = platform_get_drvdata(pdev);return uart_remove_one_port(&imx_reg, &sport->port);
}

• 用于和device tree匹配的match table

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);

对应串口驱动的移植步骤中，定义并注册uart driver

在驱动init函数中注册了uart driver

int ret = uart_register_driver(&imx_reg);

在linux serial framework中，uart driver是一个平行于platform driver的概念，用于驱动“虚拟”的“串口”设备。

#define DRIVER_NAME "IMX-uart"static struct uart_driver imx_reg = {.owner          = THIS_MODULE,.driver_name    = DRIVER_NAME,.dev_name       = DEV_NAME,.major          = SERIAL_IMX_MAJOR,.minor          = MINOR_START,.nr             = ARRAY_SIZE(imx_ports),.cons           = IMX_CONSOLE,
};

对应串口驱动的移植步骤中，注册uart port

假如一个soc中有5个串口控制器（也可称作uart控制器，后面我们不再区分），每个uart控制器都可引出一个串口（uart port）。那么：
每个uart控制器，都是一个platform device，由dts文件的一个node描述。而这5个platform device，可由同一个driver驱动，即platform driver。
相对于uart控制器实实在在的存在，我们更为熟悉的串口（uart port），则是虚拟的设备，它们由“struct uart_port”描述（后面会介绍），并在platform driver的probe接口中，注册到kernel。它们可由同一个driver驱动，即这里所说的uart driver。

struct imx_port {struct uart_port	port;struct timer_list	timer;unsigned int		old_status;unsigned int		have_rtscts:1;unsigned int		dte_mode:1;unsigned int		irda_inv_rx:1;unsigned int		irda_inv_tx:1;unsigned short		trcv_delay; /* transceiver delay */struct clk		*clk_ipg;struct clk		*clk_per;const struct imx_uart_data *devdata;/* DMA fields */unsigned int		dma_is_inited:1;unsigned int		dma_is_enabled:1;unsigned int		dma_is_rxing:1;unsigned int		dma_is_txing:1;struct dma_chan		*dma_chan_rx, *dma_chan_tx;struct scatterlist	tx_sgl[2];struct imx_dma_rxbuf	rx_buf;unsigned int		tx_bytes;unsigned int		dma_tx_nents;struct delayed_work	tsk_dma_tx;wait_queue_head_t	dma_wait;unsigned int            saved_reg[10];
#define DMA_TX_IS_WORKING 1unsigned long		flags;
};

在platform driver的probe函数中会动态分配并注册一个uart port（struct uart_port）然后初始化并注册其中的port变量。初始化完之后，直接调用uart_add_one_port接口，将该port添加到kernel serial core

再返回上面的static int serial_imx_probe(struct platform_device *pdev)展开看到

//分配struct xxx_port类型的指针
struct imx_port *sport;
sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);

//获取中断号，该串口对应的中断号， 一般是从DTS中解析得到的；rxirq = platform_get_irq(pdev, 0);txirq = platform_get_irq(pdev, 1);rtsirq = platform_get_irq(pdev, 2);
//初始化并注册其中的port变量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;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;

在proble函数的最后，调用uart_add_one_port接口，将该port添加到kernel serial core
return uart_add_one_port(&imx_reg, &sport->port);

对应串口驱动的移植步骤中，定义并实现uart ops

上面platform driver的probe函数serial_imx_probe，展开中看到
sport->port.ops = &imx_pops;
struct uart_ops结构包含了各式各样的uart端口的操作函数，需要在添加uart port的时候提供。

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
};

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#参考
http://www.wowotech.net/x_project/serial_driver_porting_1.html
http://www.wowotech.net/x_project/serial_driver_porting_2.html
http://www.wowotech.net/x_project/serial_driver_porting_3.html
http://www.wowotech.net/x_project/serial_driver_porting_4.html

http://www.wowotech.net/comm/serial_overview.html