From: Ilpo Järvinen ilpo.jarvinen@linux.intel.com
[ Upstream commit f58c252e30cf74f68b0054293adc03b5923b9f0e ]
When 8250 UART is using DMA, x_char (XON/XOFF) is never sent to the wire. After this change, x_char is injected correctly.
Create uart_xchar_out() helper for sending the x_char out and accounting related to it. It seems that almost every driver does these same steps with x_char. Except for 8250, however, almost all currently lack .serial_out so they cannot immediately take advantage of this new helper.
The downside of this patch is that it might reintroduce the problems some devices faced with mixed DMA/non-DMA transfer which caused revert f967fc8f165f (Revert "serial: 8250_dma: don't bother DMA with small transfers"). However, the impact should be limited to cases with XON/XOFF (that didn't work with DMA capable devices to begin with so this problem is not very likely to cause a major issue, if any at all).
Fixes: 9ee4b83e51f74 ("serial: 8250: Add support for dmaengine") Reported-by: Gilles Buloz gilles.buloz@kontron.com Tested-by: Gilles Buloz gilles.buloz@kontron.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Link: https://lore.kernel.org/r/20220314091432.4288-2-ilpo.jarvinen@linux.intel.co... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/8250/8250_dma.c | 11 ++++++++++- drivers/tty/serial/8250/8250_port.c | 4 +--- drivers/tty/serial/serial_core.c | 14 ++++++++++++++ include/linux/serial_core.h | 2 ++ 4 files changed, 27 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c index 890fa7ddaa7f..b3c3f7e5851a 100644 --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -64,10 +64,19 @@ int serial8250_tx_dma(struct uart_8250_port *p) struct uart_8250_dma *dma = p->dma; struct circ_buf *xmit = &p->port.state->xmit; struct dma_async_tx_descriptor *desc; + struct uart_port *up = &p->port; int ret;
- if (dma->tx_running) + if (dma->tx_running) { + if (up->x_char) { + dmaengine_pause(dma->txchan); + uart_xchar_out(up, UART_TX); + dmaengine_resume(dma->txchan); + } return 0; + } else if (up->x_char) { + uart_xchar_out(up, UART_TX); + }
if (uart_tx_stopped(&p->port) || uart_circ_empty(xmit)) { /* We have been called from __dma_tx_complete() */ diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index fd0339d22491..9f116e75956e 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1819,9 +1819,7 @@ void serial8250_tx_chars(struct uart_8250_port *up) int count;
if (port->x_char) { - serial_out(up, UART_TX, port->x_char); - port->icount.tx++; - port->x_char = 0; + uart_xchar_out(port, UART_TX); return; } if (uart_tx_stopped(port)) { diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 0db90be4c3bc..f67540ae2a88 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -644,6 +644,20 @@ static void uart_flush_buffer(struct tty_struct *tty) tty_port_tty_wakeup(&state->port); }
+/* + * This function performs low-level write of high-priority XON/XOFF + * character and accounting for it. + * + * Requires uart_port to implement .serial_out(). + */ +void uart_xchar_out(struct uart_port *uport, int offset) +{ + serial_port_out(uport, offset, uport->x_char); + uport->icount.tx++; + uport->x_char = 0; +} +EXPORT_SYMBOL_GPL(uart_xchar_out); + /* * This function is used to send a high-priority XON/XOFF character to * the device diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index c58cc142d23f..8c32935e1059 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -458,6 +458,8 @@ extern void uart_handle_cts_change(struct uart_port *uport, extern void uart_insert_char(struct uart_port *port, unsigned int status, unsigned int overrun, unsigned int ch, unsigned int flag);
+void uart_xchar_out(struct uart_port *uport, int offset); + #ifdef CONFIG_MAGIC_SYSRQ_SERIAL #define SYSRQ_TIMEOUT (HZ * 5)