linux-kernel - [PATCH] tty: serial: fsl_lpuart: Fix Tx DMA edge case

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Date:   Thu,  6 Oct 2016 15:13:04 -0700
From:   Aaron Brice <aaron.brice@...asoft.com>
To:     gregkh@...uxfoundation.org, jslaby@...e.com,
        bhuvanchandra.dv@...adex.com, stefan@...er.ch
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] tty: serial: fsl_lpuart: Fix Tx DMA edge case

In the case where head == 0 on the circular buffer, there should be one
DMA buffer, not two.  The second zero-length buffer would break the
lpuart driver, transfer would never complete.

Signed-off-by: Aaron Brice <aaron.brice@...asoft.com>
---
 drivers/tty/serial/fsl_lpuart.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index de9d510..76103f2 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -328,7 +328,7 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
 
 	sport->dma_tx_bytes = uart_circ_chars_pending(xmit);
 
-	if (xmit->tail < xmit->head) {
+	if (xmit->tail < xmit->head || xmit->head == 0) {
 		sport->dma_tx_nents = 1;
 		sg_init_one(sgl, xmit->buf + xmit->tail, sport->dma_tx_bytes);
 	} else {
@@ -359,7 +359,6 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
 	sport->dma_tx_in_progress = true;
 	sport->dma_tx_cookie = dmaengine_submit(sport->dma_tx_desc);
 	dma_async_issue_pending(sport->dma_tx_chan);
-
 }
 
 static void lpuart_dma_tx_complete(void *arg)
-- 
2.7.4