Blackfin Serial Driver: fix error while transferring large files

Ignore receiving data if new position is in the same line of current
buffer tail and is small.  This should decrease overruns.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 29 insertions, 2 deletions

diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
index d86123e03391..65a4c07f6199 100644
--- a/drivers/serial/bfin_5xx.c
+++ b/drivers/serial/bfin_5xx.c
@@ -477,6 +477,15 @@ void bfin_serial_rx_dma_timeout(struct bfin_serial_port *uart)
 
         spin_lock_irqsave(&uart->port.lock, flags);
 
+        /* 2D DMA RX buffer ring is used. Because curr_y_count and
+         * curr_x_count can't be read as an atomic operation,
+         * curr_y_count should be read before curr_x_count. When
+         * curr_x_count is read, curr_y_count may already indicate
+         * next buffer line. But, the position calculated here is
+         * still indicate the old line. The wrong position data may
+         * be smaller than current buffer tail, which cause garbages
+         * are received if it is not prohibit.
+         */
         uart->rx_dma_nrows = get_dma_curr_ycount(uart->rx_dma_channel);
         x_pos = get_dma_curr_xcount(uart->rx_dma_channel);
         uart->rx_dma_nrows = DMA_RX_YCOUNT - uart->rx_dma_nrows;
@@ -487,7 +496,11 @@ void bfin_serial_rx_dma_timeout(struct bfin_serial_port *uart)
                 x_pos = 0;
 
         pos = uart->rx_dma_nrows * DMA_RX_XCOUNT + x_pos;
-        if (pos != uart->rx_dma_buf.tail) {
+        /* Ignore receiving data if new position is in the same line of
+         * current buffer tail and small.
+         */
+        if (pos > uart->rx_dma_buf.tail ||
+                uart->rx_dma_nrows < (uart->rx_dma_buf.tail/DMA_RX_XCOUNT)) {
                 uart->rx_dma_buf.head = pos;
                 bfin_serial_dma_rx_chars(uart);
                 uart->rx_dma_buf.tail = uart->rx_dma_buf.head;
@@ -532,11 +545,25 @@ static irqreturn_t bfin_serial_dma_rx_int(int irq, void *dev_id)
 {
         struct bfin_serial_port *uart = dev_id;
         unsigned short irqstat;
+        int pos;
 
         spin_lock(&uart->port.lock);
         irqstat = get_dma_curr_irqstat(uart->rx_dma_channel);
         clear_dma_irqstat(uart->rx_dma_channel);
-        bfin_serial_dma_rx_chars(uart);
+
+        uart->rx_dma_nrows = get_dma_curr_ycount(uart->rx_dma_channel);
+        uart->rx_dma_nrows = DMA_RX_YCOUNT - uart->rx_dma_nrows;
+        if (uart->rx_dma_nrows == DMA_RX_YCOUNT)
+                uart->rx_dma_nrows = 0;
+
+        pos = uart->rx_dma_nrows * DMA_RX_XCOUNT;
+        if (pos > uart->rx_dma_buf.tail ||
+                uart->rx_dma_nrows < (uart->rx_dma_buf.tail/DMA_RX_XCOUNT)) {
+                uart->rx_dma_buf.head = pos;
+                bfin_serial_dma_rx_chars(uart);
+                uart->rx_dma_buf.tail = uart->rx_dma_buf.head;
+        }
+
         spin_unlock(&uart->port.lock);
 
         return IRQ_HANDLED;