Commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") introduced an error in the TX DMA handling for 8250_omap.
When the OMAP_DMA_TX_KICK flag is set, one byte is pulled from the kfifo and emitted directly in order to start the DMA. This is done without updating DMA tx_size which leads to uart_xmit_advance() called in the DMA complete callback advancing the kfifo by one too much.
In practice, transmitting N bytes has been seen to result in the last N-1 bytes being sent repeatedly.
This change fixes the problem by moving all of the dma setup after the OMAP_DMA_TX_KICK handling and using kfifo_len() instead of the dma size for the 4-byte cutoff check. This slightly changes the behaviour at buffer wraparound, but it still transmits the correct bytes somehow. At the point kfifo_dma_out_prepare_mapped is called, at least one byte is guaranteed to be in the fifo, so checking the return value is not necessary.
Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") Cc: stable@vger.kernel.org Signed-off-by: Mans Rullgard mans@mansr.com --- v2: split patch in two --- drivers/tty/serial/8250/8250_omap.c | 24 +++++++++--------------- 1 file changed, 9 insertions(+), 15 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index f1aee915bc02..180466e09605 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -1173,16 +1173,6 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) return 0; }
- sg_init_table(&sg, 1); - ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, - UART_XMIT_SIZE, dma->tx_addr); - if (ret != 1) { - serial8250_clear_THRI(p); - return 0; - } - - dma->tx_size = sg_dma_len(&sg); - if (priv->habit & OMAP_DMA_TX_KICK) { unsigned char c; u8 tx_lvl; @@ -1207,7 +1197,7 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) ret = -EBUSY; goto err; } - if (dma->tx_size < 4) { + if (kfifo_len(&tport->xmit_fifo) < 4) { ret = -EINVAL; goto err; } @@ -1216,11 +1206,12 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) goto err; } skip_byte = c; - /* now we need to recompute due to kfifo_get */ - kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, - UART_XMIT_SIZE, dma->tx_addr); }
+ sg_init_table(&sg, 1); + kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1, + UART_XMIT_SIZE, dma->tx_addr); + desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT | DMA_CTRL_ACK); if (!desc) { @@ -1228,6 +1219,7 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) goto err; }
+ dma->tx_size = sg_dma_len(&sg); dma->tx_running = 1;
desc->callback = omap_8250_dma_tx_complete; @@ -1248,8 +1240,10 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) err: dma->tx_err = 1; out_skip: - if (skip_byte >= 0) + if (skip_byte >= 0) { serial_out(p, UART_TX, skip_byte); + p->port.icount.tx++; + } return ret; }