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 <[email protected]>
>
> CC: Rob Herring <[email protected]>
> CC: Pawel Moll <[email protected]>
> CC: Mark Rutland <[email protected]>
> CC: Ian Campbell <[email protected]>
> CC: Kumar Gala <[email protected]>
> CC: Randy Dunlap <[email protected]>
> CC: Greg Kroah-Hartman <[email protected]>
> CC: Jiri Slaby <[email protected]>
> CC: Santosh Shilimkar <[email protected]>
> ---
> .../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(-)
>
[...]
> 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;
>
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