Re: [PATCH v2] serial: uart: add hw flow control support configuration
From: Peter Hurley <hidden>
Date: 2014-08-07 15:29:26
Also in:
linux-serial, lkml
On 05/01/2014 03:04 PM, Murali Karicheri wrote:
8250 uart driver currently supports only software assisted hw flow control. The software assisted hw flow control maintains a hw_stopped flag in the tty structure to stop and start transmission and use modem status interrupt for the event to drive the handshake signals. This is not needed if hw has flow control capabilities. This patch adds a DT attribute for enabling hw flow control for a uart port. Also skip stop and start if this flag is present in flag field of the port structure. Signed-off-by: Murali Karicheri <redacted> CC: Rob Herring <robh+dt@kernel.org> CC: Pawel Moll <redacted> CC: Mark Rutland <mark.rutland@arm.com> CC: Ian Campbell <redacted> CC: Kumar Gala <redacted> CC: Randy Dunlap <redacted> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> CC: Jiri Slaby <redacted> CC: Santosh Shilimkar <redacted> --- .../devicetree/bindings/serial/of-serial.txt | 1 + drivers/tty/serial/8250/8250_core.c | 6 ++++-- drivers/tty/serial/of_serial.c | 4 ++++ drivers/tty/serial/serial_core.c | 12 +++++++++--- 4 files changed, 18 insertions(+), 5 deletions(-)
[...]
quoted hunk ↗ jump to hunk
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index b68550d..851707a 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c@@ -174,8 +174,12 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state, if (tty->termios.c_cflag & CBAUD) uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR); } - - if (tty_port_cts_enabled(port)) { + /* + * if hw support flow control without software intervention, + * then skip the below check + */ + if (tty_port_cts_enabled(port) && + !(uport->flags & UPF_HARD_FLOW)) { spin_lock_irq(&uport->lock); if (!(uport->ops->get_mctrl(uport) & TIOCM_CTS)) tty->hw_stopped = 1;@@ -2772,7 +2776,9 @@ void uart_handle_cts_change(struct uart_port *uport, unsigned int status) uport->icount.cts++; - if (tty_port_cts_enabled(port)) { + /* skip below code if the hw flow control is supported */ + if (tty_port_cts_enabled(port) && + !(uport->flags & UPF_HARD_FLOW)) {
Why is a modem status interrupt being generated for DCTS if autoflow control is enabled? This should be: WARN_ON_ONCE(uport->flags & UPF_HARD_FLOW); to indicate a mis-configured driver/device.
if (tty->hw_stopped) {
if (status) {
tty->hw_stopped = 0;