mxser: switch from xmit_buf to kfifo

Use kfifo for xmit buffer handling. The change is mostly
straightforward. It saves complexity both on the stuffing side
(mxser_write() and mxser_put_char()) and pulling side
(mxser_transmit_chars()). In fact, the loop in mxser_write() can be
completely deleted as the wrap of the buffer is taken care of in the
kfifo code now.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220124071430.14907-8-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
index 4ddc12a636665b0fa4829363013d11c52b36f98c..836c9eca2946a09ee707274879be43a6bcd3f085 100644 (file)
--- a/drivers/tty/mxser.c
+++ b/drivers/tty/mxser.c
@@ -275,9 +275,6 @@ struct mxser_port {
        u8 read_status_mask;
        u8 ignore_status_mask;
        u8 xmit_fifo_size;
-       unsigned int xmit_head;
-       unsigned int xmit_tail;
-       unsigned int xmit_cnt;
 
        spinlock_t slock;
 };
@@ -813,7 +810,7 @@ static int mxser_activate(struct tty_port *port, struct tty_struct *tty)
        (void) inb(info->ioaddr + UART_MSR);
 
        clear_bit(TTY_IO_ERROR, &tty->flags);
-       info->xmit_cnt = info->xmit_head = info->xmit_tail = 0;
+       kfifo_reset(&port->xmit_fifo);
 
        /*
         * and set the speed of the serial port
@@ -901,9 +898,8 @@ static void mxser_flush_buffer(struct tty_struct *tty)
        struct mxser_port *info = tty->driver_data;
        unsigned long flags;
 
-
        spin_lock_irqsave(&info->slock, flags);
-       info->xmit_cnt = info->xmit_head = info->xmit_tail = 0;
+       kfifo_reset(&info->port.xmit_fifo);
 
        outb(info->FCR | UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT,
                info->ioaddr + UART_FCR);
@@ -920,50 +916,34 @@ static void mxser_close(struct tty_struct *tty, struct file *filp)
 
 static int mxser_write(struct tty_struct *tty, const unsigned char *buf, int count)
 {
-       int c, total = 0;
        struct mxser_port *info = tty->driver_data;
        unsigned long flags;
+       int written;
+       bool is_empty;
 
-       while (1) {
-               c = min_t(int, count, min(SERIAL_XMIT_SIZE - info->xmit_cnt - 1,
-                                         SERIAL_XMIT_SIZE - info->xmit_head));
-               if (c <= 0)
-                       break;
-
-               memcpy(info->port.xmit_buf + info->xmit_head, buf, c);
-               spin_lock_irqsave(&info->slock, flags);
-               info->xmit_head = (info->xmit_head + c) &
-                                 (SERIAL_XMIT_SIZE - 1);
-               info->xmit_cnt += c;
-               spin_unlock_irqrestore(&info->slock, flags);
-
-               buf += c;
-               count -= c;
-               total += c;
-       }
+       spin_lock_irqsave(&info->slock, flags);
+       written = kfifo_in(&info->port.xmit_fifo, buf, count);
+       is_empty = kfifo_is_empty(&info->port.xmit_fifo);
+       spin_unlock_irqrestore(&info->slock, flags);
 
-       if (info->xmit_cnt && !tty->flow.stopped)
+       if (!is_empty && !tty->flow.stopped)
                if (!tty->hw_stopped || mxser_16550A_or_MUST(info))
                        mxser_start_tx(info);
 
-       return total;
+       return written;
 }
 
 static int mxser_put_char(struct tty_struct *tty, unsigned char ch)
 {
        struct mxser_port *info = tty->driver_data;
        unsigned long flags;
-
-       if (info->xmit_cnt >= SERIAL_XMIT_SIZE - 1)
-               return 0;
+       int ret;
 
        spin_lock_irqsave(&info->slock, flags);
-       info->port.xmit_buf[info->xmit_head++] = ch;
-       info->xmit_head &= SERIAL_XMIT_SIZE - 1;
-       info->xmit_cnt++;
+       ret = kfifo_put(&info->port.xmit_fifo, ch);
        spin_unlock_irqrestore(&info->slock, flags);
 
-       return 1;
+       return ret;
 }
 
 
@@ -971,7 +951,7 @@ static void mxser_flush_chars(struct tty_struct *tty)
 {
        struct mxser_port *info = tty->driver_data;
 
-       if (!info->xmit_cnt || tty->flow.stopped ||
+       if (kfifo_is_empty(&info->port.xmit_fifo) || tty->flow.stopped ||
                        (tty->hw_stopped && !mxser_16550A_or_MUST(info)))
                return;
 
@@ -981,16 +961,15 @@ static void mxser_flush_chars(struct tty_struct *tty)
 static unsigned int mxser_write_room(struct tty_struct *tty)
 {
        struct mxser_port *info = tty->driver_data;
-       int ret;
 
-       ret = SERIAL_XMIT_SIZE - info->xmit_cnt - 1;
-       return ret < 0 ? 0 : ret;
+       return kfifo_avail(&info->port.xmit_fifo);
 }
 
 static unsigned int mxser_chars_in_buffer(struct tty_struct *tty)
 {
        struct mxser_port *info = tty->driver_data;
-       return info->xmit_cnt;
+
+       return kfifo_len(&info->port.xmit_fifo);
 }
 
 /*
@@ -1379,7 +1358,7 @@ static void mxser_start(struct tty_struct *tty)
        unsigned long flags;
 
        spin_lock_irqsave(&info->slock, flags);
-       if (info->xmit_cnt)
+       if (!kfifo_is_empty(&info->port.xmit_fifo))
                __mxser_start_tx(info);
        spin_unlock_irqrestore(&info->slock, flags);
 }
@@ -1610,7 +1589,7 @@ static void mxser_transmit_chars(struct tty_struct *tty, struct mxser_port *port
                return;
        }
 
-       if (!port->xmit_cnt || tty->flow.stopped ||
+       if (kfifo_is_empty(&port->port.xmit_fifo) || tty->flow.stopped ||
                        (tty->hw_stopped && !mxser_16550A_or_MUST(port))) {
                __mxser_stop_tx(port);
                return;
@@ -1618,18 +1597,19 @@ static void mxser_transmit_chars(struct tty_struct *tty, struct mxser_port *port
 
        count = port->xmit_fifo_size;
        do {
-               outb(port->port.xmit_buf[port->xmit_tail++],
-                       port->ioaddr + UART_TX);
-               port->xmit_tail &= SERIAL_XMIT_SIZE - 1;
-               port->icount.tx++;
-               if (!--port->xmit_cnt)
+               unsigned char c;
+
+               if (!kfifo_get(&port->port.xmit_fifo, &c))
                        break;
+
+               outb(c, port->ioaddr + UART_TX);
+               port->icount.tx++;
        } while (--count > 0);
 
-       if (port->xmit_cnt < WAKEUP_CHARS)
+       if (kfifo_len(&port->port.xmit_fifo) < WAKEUP_CHARS)
                tty_wakeup(tty);
 
-       if (!port->xmit_cnt)
+       if (kfifo_is_empty(&port->port.xmit_fifo))
                __mxser_stop_tx(port);
 }