本文主要是介绍8250驱动使用workqueue加入RS485控制逻辑，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
项目中使用了RS485，主控是PX30
查看资料，有些前辈的帖子写了用了tasklet 中断服务来做，无法休眠，
于是使用了workqueue来进行延迟检测操作，主要是为了检查是否数据发送完毕，数据发送完后就拉低IO口。
在结构体中新增定义：
diff --git a/kernel/include/linux/serial_8250.h b/kernel/include/linux/serial_8250.h
old mode 100644
new mode 100755
index faa0e03..058dafd
--- a/kernel/include/linux/serial_8250.h
+++ b/kernel/include/linux/serial_8250.h
@@ -40,6 +40,7 @@ struct plat_serial8250_port {void (*pm)(struct uart_port *, unsigned int state,unsigned old);void (*handle_break)(struct uart_port *);
+};/*
@@ -122,6 +123,12 @@ struct uart_8250_port {/* 8250 specific callbacks */int (*dl_read)(struct uart_8250_port *);void (*dl_write)(struct uart_8250_port *, int);
+ /*add by laowang, add gpio-rs485 ctrl*/
+ int rs485_gpio;
+ int rs485_enable;
+ struct work_struct rs485x_work;
+ struct workqueue_struct *rs485x_work_delay;
+ /*end of gpio-rs485 ctrl*/ };
其中rs485_gpio 和 rs485_enable 通过设备树进行配置，既然是固有的产品上使用，就不使用IOCTL来传参，
让使用者直接当个串口来用。
-
+#include <linux/of_gpio.h>#include <asm/byteorder.h>#include "8250.h"
@@ -67,6 +67,7 @@ struct dw8250_data {unsigned int skip_autocfg:1;unsigned int uart_16550_compatible:1;
+};#define BYT_PRV_CLK 0x800
@@ -402,6 +403,8 @@ static int dw8250_probe(struct platform_device *pdev)struct resource *regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);int irq = platform_get_irq(pdev, 0);struct uart_port *p = &uart.port;
+ struct device_node *np;// = p->dev->of_node;
+struct dw8250_data *data;int err;u32 val;
@@ -543,6 +546,22 @@ static int dw8250_probe(struct platform_device *pdev)uart.dma = &data->dma;}+
+/***********************add rs485 gpio ctrl*********************************/
+ np = p->dev->of_node;
+ of_property_read_u32(np, "rs485enable",&(uart.rs485_enable));
+ if(uart.rs485_enable == 1)
+ {
+ uart.rs485_gpio = of_get_named_gpio(np, "rs485gpio", 0);
+ }
+
+ printk(KERN_INFO "wjxprint uartline: %d (rs485en = %d, rs485gpio = %d)\n",
+ p->line,
+ uart.rs485_enable,
+ uart.rs485_gpio);
+
+/***********************end add rs485 gpio ctrl*********************************/
+data->line = serial8250_register_8250_port(&uart);
初始化注册：
register_dev_spec_attr_grp(up);up->fcr = uart_config[up->port.type].fcr;
+
+
+ if (up->rs485_enable)
+ {
+ printk(KERN_INFO "uart %d set 485 on address %lx\n", up->port.line,(unsigned long)port);
+ switch(up->port.line)
+ {
+ case 0:
+ up->rs485x_work_delay = create_singlethread_workqueue("rs4853_work_delay");
+ flush_workqueue(up->rs485x_work_delay);
+ INIT_WORK(&up->rs485x_work, serial8250_4853_do_workqueue);
+ break;
这里注册了一个工作队列。
发送数据前拉高IO：
@@ -1489,6 +1635,17 @@ void serial8250_tx_chars(struct uart_8250_port *up)}count = up->tx_loadsz;
+ if(count > 0)
+ {
+ if(up->rs485_enable == 1)
+ {
+ // printk(KERN_WARNING "ttyS: serial8250_start_tx: in line %d \n",up->port.line);
+ gpio_set_value(up->rs485_gpio,1);
+
+ // udelay(100);
+ }
+ }
+do {serial_out(up, UART_TX, xmit->buf[xmit->tail]);xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
发送数据结束触发工作队列：
if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
@@ -1513,7 +1671,18 @@ void serial8250_tx_chars(struct uart_8250_port *up)* the interrupt and RPM in __stop_tx()*/if (uart_circ_empty(xmit) && !(up->capabilities & UART_CAP_RPM))
+ {__stop_tx(up);
+
+ if(up->rs485_enable == 1)
+ {
+ // printk(KERN_WARNING
+ // "ttyS%d: __stop_tx end print by wjx \n",
+ // up->port.line);
+ // tasklet_hi_schedule(&(up->rs485x_tasklet));
+ queue_work(up->rs485x_work_delay, &(up->rs485x_work));
+ }
+ }}EXPORT_SYMBOL_GPL(serial8250_tx_chars);
服务程序：
+static void serial8250_4851_do_workqueue(struct work_struct *work);
+
+static inline void handl_tx_485x(struct uart_8250_port * param)
+{
+ struct uart_8250_port *p ;//= up_to_u8250p((struct uart_port *)param);
+ struct uart_port *port = 0 ;
+
+
+ struct uart_state *state = 0;
+ struct tty_struct *tty = 0;
+ struct ktermios termios;
+ unsigned int baud = 0;
+ int bit_width = 0;
+
+ struct circ_buf *xmit;// = &port->state->xmit;
+ unsigned long flags;
+ unsigned int lsr;
+// printk(KERN_WARNING "ttyS: serial8250_4851_do_tasklet port in param: %lx \n",(unsigned long )&(param->port));
+ p = param;
+ //p = up_to_u8250p(port);
+ port = &(p->port);
+
+ if(port == 0)
+ {
+ printk(KERN_WARNING "error in port ttyS: handl_tx_485x port in param: line is %lx :%d \n",(unsigned long )param,p->port.line);
+ return;
+ }
+
+ //p = up_to_u8250p((struct uart_port *)param);
+
+ xmit = &port->state->xmit;
+
+ //printk(KERN_WARNING "ttyS: serial8250_4851_do_tasklet port in param: line is %lx :%d \n",param,p->port.line);
+ #if 1
+ while (1)
+ {
+
+ spin_lock_irqsave(&port->lock, flags);
+ lsr = serial_port_in(port, UART_LSR);
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ if (uart_circ_empty(xmit) && ((lsr & BOTH_EMPTY) == BOTH_EMPTY))
+ {
+ break;
+ }
+ // if(serial8250_tx_empty(port) == TIOCSER_TEMT)
+ // {
+ // break;
+ // }
+ // else
+ // {
+ // udelay(10);
+ // }
+
+ }
+ #else
+ while (port->ops->tx_empty(port) != TIOCSER_TEMT)
+ {
+ ;
+ }
+ #endif
+
+ state = port->state;//container_of(port, struct uart_state, uart_port);
+ tty = port->state->port.tty; //container_of(state, struct tty_struct, driver_data);
+ termios = tty->termios;
+ baud = uart_get_baud_rate(port, &termios, NULL, 1200, 115200);
+ bit_width = (baud > 0) ? 1000000/baud : 0;
+ // bit_width = (bit_width > 50) ? (bit_width-50) : 0; // Measured delay value is 50 us
+
+ udelay(bit_width); // a stop bit
+ //printk(KERN_WARNING "ttyS: serial8250_4851_do_tasklet bit_width : %d \n",bit_width);
+ gpio_set_value(p->rs485_gpio,0);
+ //gpio_485_set_value(false);
+
+}
+
+
+static void serial8250_4851_do_workqueue(struct work_struct *work)
+{
+ struct uart_8250_port *data = container_of(work, struct uart_8250_port,
+ rs485x_work);
+ handl_tx_485x(data);
+
+}
当前测试收发正常稳定。
但是我系统里有4个串口都需要做485，搞了笨方法，4个workqueue，不知是否有更好的方案可以做。
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