| Message ID | 20250430163709.15850-1-mans@mansr.com |
|---|---|
| State | New |
| Headers | show |
| Series | tty: serial: 8250_omap: fix tx with dma | expand |
CC omap On Wed, 30 Apr 2025 at 18:45, Mans Rullgard <mans@mansr.com> wrote: > Commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") > introduced two errors in the TX DMA handling for 8250_omap. > > Firstly, kfifo_dma_out_prepare_mapped() needs a scatterlist with two > entries whereas only one is provided. The same error was fixed for > 8250_dma in 59449c9dbdaa ("tty: serial: 8250_dma: use sgl with 2 nents > to take care of buffer wrap"). > > Secondly, 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 both problems. > > Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") > Signed-off-by: Mans Rullgard <mans@mansr.com> > --- > drivers/tty/serial/8250/8250_omap.c | 35 +++++++++++++++-------------- > 1 file changed, 18 insertions(+), 17 deletions(-) > > diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c > index f1aee915bc02..84a2f013015e 100644 > --- a/drivers/tty/serial/8250/8250_omap.c > +++ b/drivers/tty/serial/8250/8250_omap.c > @@ -1152,9 +1152,11 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) > struct omap8250_priv *priv = p->port.private_data; > struct tty_port *tport = &p->port.state->port; > struct dma_async_tx_descriptor *desc; > - struct scatterlist sg; > + struct scatterlist *sg; > + struct scatterlist sgl[2]; > int skip_byte = -1; > int ret; > + int i; > > if (dma->tx_running) > return 0; > @@ -1173,16 +1175,6 @@ 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 +1199,7 @@ 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; > } > @@ -1216,12 +1208,19 @@ 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); > } > > - desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, DMA_MEM_TO_DEV, > + sg_init_table(sgl, ARRAY_SIZE(sgl)); > + > + ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, sgl, ARRAY_SIZE(sgl), > + UART_XMIT_SIZE, dma->tx_addr); > + > + dma->tx_size = 0; > + > + for_each_sg(sgl, sg, ret, i) > + dma->tx_size += sg_dma_len(sg); > + > + desc = dmaengine_prep_slave_sg(dma->txchan, sgl, ret, DMA_MEM_TO_DEV, > DMA_PREP_INTERRUPT | DMA_CTRL_ACK); > if (!desc) { > ret = -EBUSY; > @@ -1248,8 +1247,10 @@ 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; > } > > -- > 2.49.0 Gr{oetje,eeting}s, Geert
On 30. 04. 25, 18:37, Mans Rullgard wrote: > Commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") > introduced two errors in the TX DMA handling for 8250_omap. > > Firstly, kfifo_dma_out_prepare_mapped() needs a scatterlist with two > entries whereas only one is provided. The same error was fixed for > 8250_dma in 59449c9dbdaa ("tty: serial: 8250_dma: use sgl with 2 nents > to take care of buffer wrap"). It's not an error. This is how it used to work since ever. Providing two is an optimization, right? > Secondly, 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 Ah, that's an error, of course. > 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 both problems. I am not sure you want to mix fixups with features. > Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") > Signed-off-by: Mans Rullgard <mans@mansr.com> ... > @@ -1248,8 +1247,10 @@ 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++; This is unrelated (but correct) too. thanks,
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index f1aee915bc02..84a2f013015e 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -1152,9 +1152,11 @@ static int omap_8250_tx_dma(struct uart_8250_port *p) struct omap8250_priv *priv = p->port.private_data; struct tty_port *tport = &p->port.state->port; struct dma_async_tx_descriptor *desc; - struct scatterlist sg; + struct scatterlist *sg; + struct scatterlist sgl[2]; int skip_byte = -1; int ret; + int i; if (dma->tx_running) return 0; @@ -1173,16 +1175,6 @@ 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 +1199,7 @@ 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; } @@ -1216,12 +1208,19 @@ 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); } - desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, DMA_MEM_TO_DEV, + sg_init_table(sgl, ARRAY_SIZE(sgl)); + + ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, sgl, ARRAY_SIZE(sgl), + UART_XMIT_SIZE, dma->tx_addr); + + dma->tx_size = 0; + + for_each_sg(sgl, sg, ret, i) + dma->tx_size += sg_dma_len(sg); + + desc = dmaengine_prep_slave_sg(dma->txchan, sgl, ret, DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT | DMA_CTRL_ACK); if (!desc) { ret = -EBUSY; @@ -1248,8 +1247,10 @@ 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; }
Commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") introduced two errors in the TX DMA handling for 8250_omap. Firstly, kfifo_dma_out_prepare_mapped() needs a scatterlist with two entries whereas only one is provided. The same error was fixed for 8250_dma in 59449c9dbdaa ("tty: serial: 8250_dma: use sgl with 2 nents to take care of buffer wrap"). Secondly, 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 both problems. Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") Signed-off-by: Mans Rullgard <mans@mansr.com> --- drivers/tty/serial/8250/8250_omap.c | 35 +++++++++++++++-------------- 1 file changed, 18 insertions(+), 17 deletions(-)