[PATCH 05/18] Blackfin Serial Driver: fix bug - serial port transfer big file from host to target would have more lines

[Bryan Wu <cooloney@kernel.org>]

From: Sonic Zhang <sonic.zhang@analog.com>

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

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
---
 drivers/serial/bfin_5xx.c |   31 +++++++++++++++++++++++++++++--
 1 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
index 8d34ccd..5a163f6 100644
--- a/drivers/serial/bfin_5xx.c
+++ b/drivers/serial/bfin_5xx.c
@@ -407,6 +407,15 @@ 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;
@@ -417,7 +426,11 @@ 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;
@@ -455,11 +468,25 @@ 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;
-- 
1.5.6.3