Hi Shreyas,
On 10/31/2014 04:33 PM, Shreyas Bethur wrote:
> When tty port is opened, we will raise the DTR and RTS lines. But for
> second and subsequent opens, we should not modify these lines because the
> first session might be actively using these lines. We don't want a second
> open to interfere with the first session.
>
> Signed-off-by: Shreyas Bethur <shreyas.bethur@xxxxxx>
> ---
> To give some background for this patch, we have a product that uses the
> DTR line on the serial port for synchronization with other devices. While
> the synchronization application is using the DTR line, if another process
> opens the same port, then DTR line is raised, and thus interferes with the
> synchronization application. So, if a port is open, subsequent opens
> should not modify any modem lines.
Would you please expand on your use-case?
Regards,
Peter Hurley
> This patch is my attempt to fix this issue. Please review my fix, and let
> me know what you folks think.
> ---
> drivers/tty/tty_port.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
> index 1b93357..8a6c80a 100644
> --- a/drivers/tty/tty_port.c
> +++ b/drivers/tty/tty_port.c
> @@ -363,6 +363,7 @@ int tty_port_block_til_ready(struct tty_port *port,
> int do_clocal = 0, retval;
> unsigned long flags;
> DEFINE_WAIT(wait);
> + bool port_first_open = true;
>
> /* block if port is in the process of being closed */
> if (port->flags & ASYNC_CLOSING) {
> @@ -381,8 +382,15 @@ int tty_port_block_til_ready(struct tty_port *port,
> return 0;
> }
> if (filp->f_flags & O_NONBLOCK) {
> - /* Indicate we are open */
> - if (tty->termios.c_cflag & CBAUD)
> + /* The port lock protects the port counts */
> + spin_lock_irqsave(&port->lock, flags);
> + if (port->count > 1)
> + port_first_open = false;
> + spin_unlock_irqrestore(&port->lock, flags);
> +
> + /* Indicate we are open. Raise DTR and RTS only if opening
> the
> + port for the first time */
> + if ((tty->termios.c_cflag & CBAUD) && port_first_open)
> tty_port_raise_dtr_rts(port);
> port->flags |= ASYNC_NORMAL_ACTIVE;
> return 0;
>
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