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.
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;
--
1.9.1
--
--
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