[PATCH 1/1][SRU][M][Unstable] UBUNTU: SAUCE: platform/x86: dell-uart-backlight: replace chars_in_buffer() with flush_chars()

[AceLan Kao]

From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/2032174

After v6.5, calls tty->driver->ops->chars_in_buffer() may lead to a
deadlock and got soft lockup error. Try using tty->driver->ops->flush_chars()
to archive to same scenario.

There is no functional change, even if uart_flush_chars() doesn't do what
we expected, the driver should be able to keep working, as the backlight
commands is only 3 or 4 bytes short and has little chance to stay in the
queue partially.

Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao at canonical.com>
---
 drivers/platform/x86/dell/dell-uart-backlight.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
index 3f8ea639d557..120701e5b8b1 100644
--- a/drivers/platform/x86/dell/dell-uart-backlight.c
+++ b/drivers/platform/x86/dell/dell-uart-backlight.c
@@ -39,7 +39,8 @@ static struct file *ftty;
 
 unsigned int (*io_serial_in)(struct uart_port *p, int offset);
 int (*uart_write)(struct tty_struct *tty, const unsigned char *buf, int count);
-unsigned int (*uart_chars_in_buffer)(struct tty_struct *tty);
+void (*uart_flush_chars)(struct tty_struct *tty);
+
 
 static bool force;
 module_param(force, bool, 0444);
@@ -160,8 +161,7 @@ static int dell_uart_write(struct uart_8250_port *up, __u8 *buf, int len)
 	tty_port_tty_wakeup(&port->state->port);
 	tty = tty_port_tty_get(&port->state->port);
 	actual = uart_write(tty, buf, len);
-	while (uart_chars_in_buffer(tty))
-		udelay(10);
+	uart_flush_chars(tty);
 
 	return actual;
 }
@@ -401,7 +401,7 @@ static int dell_uart_startup(struct dell_uart_backlight *dell_pdata)
 	tty = port->state->port.tty;
 	io_serial_in = port->serial_in;
 	uart_write = tty->driver->ops->write;
-	uart_chars_in_buffer = tty->driver->ops->chars_in_buffer;
+	uart_flush_chars = tty->driver->ops->flush_chars;
 
 	return 0;
 }
-- 
2.34.1