synclink_gt: fix transmit DMA stall

Fix transmit DMA stall when write() called in window after previous
transmit DMA completes but before previous serial transmission completes.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 46 insertions, 29 deletions

diff --git a/drivers/char/synclink_gt.c b/drivers/char/synclink_gt.c
index 372a37e25620..bbb7f1292665 100644
--- a/drivers/char/synclink_gt.c
+++ b/drivers/char/synclink_gt.c
@@ -1,5 +1,5 @@
 /*
- * $Id: synclink_gt.c,v 4.36 2006/08/28 20:47:14 paulkf Exp $
+ * $Id: synclink_gt.c,v 4.50 2007/07/25 19:29:25 paulkf Exp $
  *
  * Device driver for Microgate SyncLink GT serial adapters.
  *
@@ -93,7 +93,7 @@
  * module identification
  */
 static char *driver_name     = "SyncLink GT";
-static char *driver_version  = "$Revision: 4.36 $";
+static char *driver_version  = "$Revision: 4.50 $";
 static char *tty_driver_name = "synclink_gt";
 static char *tty_dev_prefix  = "ttySLG";
 MODULE_LICENSE("GPL");
@@ -477,6 +477,7 @@ static void tx_set_idle(struct slgt_info *info);
 static unsigned int free_tbuf_count(struct slgt_info *info);
 static void reset_tbufs(struct slgt_info *info);
 static void tdma_reset(struct slgt_info *info);
+static void tdma_start(struct slgt_info *info);
 static void tx_load(struct slgt_info *info, const char *buf, unsigned int count);
 
 static void get_signals(struct slgt_info *info);
@@ -904,6 +905,8 @@ start:
                 spin_lock_irqsave(&info->lock,flags);
                 if (!info->tx_active)
                         tx_start(info);
+                else
+                        tdma_start(info);
                 spin_unlock_irqrestore(&info->lock,flags);
         }
 
@@ -3871,44 +3874,58 @@ static void tx_start(struct slgt_info *info)
                         slgt_irq_on(info, IRQ_TXUNDER + IRQ_TXIDLE);
                         /* clear tx idle and underrun status bits */
                         wr_reg16(info, SSR, (unsigned short)(IRQ_TXIDLE + IRQ_TXUNDER));
-
-                        if (!(rd_reg32(info, TDCSR) & BIT0)) {
-                                /* tx DMA stopped, restart tx DMA */
-                                tdma_reset(info);
-                                /* set 1st descriptor address */
-                                wr_reg32(info, TDDAR, info->tbufs[info->tbuf_start].pdesc);
-                                switch(info->params.mode) {
-                                case MGSL_MODE_RAW:
-                                case MGSL_MODE_MONOSYNC:
-                                case MGSL_MODE_BISYNC:
-                                        wr_reg32(info, TDCSR, BIT2 + BIT0); /* IRQ + DMA enable */
-                                        break;
-                                default:
-                                        wr_reg32(info, TDCSR, BIT0); /* DMA enable */
-                                }
-                        }
-
                         if (info->params.mode == MGSL_MODE_HDLC)
                                 mod_timer(&info->tx_timer, jiffies +
                                                 msecs_to_jiffies(5000));
                 } else {
-                        tdma_reset(info);
-                        /* set 1st descriptor address */
-                        wr_reg32(info, TDDAR, info->tbufs[info->tbuf_start].pdesc);
-
                         slgt_irq_off(info, IRQ_TXDATA);
                         slgt_irq_on(info, IRQ_TXIDLE);
                         /* clear tx idle status bit */
                         wr_reg16(info, SSR, IRQ_TXIDLE);
-
-                        /* enable tx DMA */
-                        wr_reg32(info, TDCSR, BIT0);
                 }
-
+                tdma_start(info);
                 info->tx_active = 1;
         }
 }
 
+/*
+ * start transmit DMA if inactive and there are unsent buffers
+ */
+static void tdma_start(struct slgt_info *info)
+{
+        unsigned int i;
+
+        if (rd_reg32(info, TDCSR) & BIT0)
+                return;
+
+        /* transmit DMA inactive, check for unsent buffers */
+        i = info->tbuf_start;
+        while (!desc_count(info->tbufs[i])) {
+                if (++i == info->tbuf_count)
+                        i = 0;
+                if (i == info->tbuf_current)
+                        return;
+        }
+        info->tbuf_start = i;
+
+        /* there are unsent buffers, start transmit DMA */
+
+        /* reset needed if previous error condition */
+        tdma_reset(info);
+
+        /* set 1st descriptor address */
+        wr_reg32(info, TDDAR, info->tbufs[info->tbuf_start].pdesc);
+        switch(info->params.mode) {
+        case MGSL_MODE_RAW:
+        case MGSL_MODE_MONOSYNC:
+        case MGSL_MODE_BISYNC:
+                wr_reg32(info, TDCSR, BIT2 + BIT0); /* IRQ + DMA enable */
+                break;
+        default:
+                wr_reg32(info, TDCSR, BIT0); /* DMA enable */
+        }
+}
+
 static void tx_stop(struct slgt_info *info)
 {
         unsigned short val;
@@ -4642,8 +4659,8 @@ static unsigned int free_tbuf_count(struct slgt_info *info)
                         i=0;
         } while (i != info->tbuf_current);
 
-        /* last buffer with zero count may be in use, assume it is */
-        if (count)
+        /* if tx DMA active, last zero count buffer is in use */
+        if (count && (rd_reg32(info, TDCSR) & BIT0))
                 --count;
 
         return count;