2016-04-12 12:52:11

by Alexandre Belloni

Subject: [PATCH] tty/serial: atmel: fix hardware handshake selection

Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
hardware handshake is enabled") actually allowed to enable hardware
handshaking.
Before, the CRTSCTS flags was silently ignored.

As the DMA controller can't drive RTS (as explain in the commit message).
Ensure that hardware flow control stays disabled when DMA is used and FIFOs
are not available.

Signed-off-by: Alexandre Belloni <[email protected]>
---
drivers/tty/serial/atmel_serial.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index d9439e6ab719..954941dd8124 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -274,6 +274,13 @@ static bool atmel_use_dma_rx(struct uart_port *port)
return atmel_port->use_dma_rx;
}

+static bool atmel_use_fifo(struct uart_port *port)
+{
+ struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
+
+ return atmel_port->fifo_size;
+}
+
static unsigned int atmel_get_lines_status(struct uart_port *port)
{
struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
@@ -2090,7 +2097,12 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
mode |= ATMEL_US_USMODE_RS485;
} else if (termios->c_cflag & CRTSCTS) {
/* RS232 with hardware handshake (RTS/CTS) */
- mode |= ATMEL_US_USMODE_HWHS;
+ if (atmel_use_dma_rx(port) && !atmel_use_fifo(port)) {
+ dev_info(port->dev, "not enabling hardware flow control because DMA is used");
+ termios->c_cflag &= ~CRTSCTS;
+ } else {
+ mode |= ATMEL_US_USMODE_HWHS;
+ }
} else {
/* RS232 without hadware handshake */
mode |= ATMEL_US_USMODE_NORMAL;
--
2.8.0.rc3

2016-04-15 12:51:59

by Nicolas Ferre

Subject: Re: [PATCH] tty/serial: atmel: fix hardware handshake selection

Le 12/04/2016 14:51, Alexandre Belloni a ?crit :
> Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
> hardware handshake is enabled") actually allowed to enable hardware
> handshaking.
> Before, the CRTSCTS flags was silently ignored.
>
> As the DMA controller can't drive RTS (as explain in the commit message).
> Ensure that hardware flow control stays disabled when DMA is used and FIFOs
> are not available.
>
> Signed-off-by: Alexandre Belloni <[email protected]>

Yes, I agree with the fix:

Acked-by: Nicolas Ferre <[email protected]>

We can also add the following tags:

Fixes: 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
hardware handshake is enabled")
Cc: stable <[email protected]> # v4.0+

Bye,

> ---
> drivers/tty/serial/atmel_serial.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index d9439e6ab719..954941dd8124 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -274,6 +274,13 @@ static bool atmel_use_dma_rx(struct uart_port *port)
> return atmel_port->use_dma_rx;
> }
>
> +static bool atmel_use_fifo(struct uart_port *port)
> +{
> + struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
> +
> + return atmel_port->fifo_size;
> +}
> +
> static unsigned int atmel_get_lines_status(struct uart_port *port)
> {
> struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
> @@ -2090,7 +2097,12 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> mode |= ATMEL_US_USMODE_RS485;
> } else if (termios->c_cflag & CRTSCTS) {
> /* RS232 with hardware handshake (RTS/CTS) */
> - mode |= ATMEL_US_USMODE_HWHS;
> + if (atmel_use_dma_rx(port) && !atmel_use_fifo(port)) {
> + dev_info(port->dev, "not enabling hardware flow control because DMA is used");
> + termios->c_cflag &= ~CRTSCTS;
> + } else {
> + mode |= ATMEL_US_USMODE_HWHS;
> + }
> } else {
> /* RS232 without hadware handshake */
> mode |= ATMEL_US_USMODE_NORMAL;
>


--
Nicolas Ferre