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。