[PATCH 0/1][SRU][M][Unstable] Got soft lockup CPU if dell_uart_backlight is probed

[AceLan Kao]

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

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

[Impact]
After v6.5, calls tty->driver->ops->chars_in_buffer() may lead to a
deadlock and got soft lockup error.

[Fix]
Do not use this function in dell-uart-backlight driver.
Try using tty->driver->ops->flush_chars() to send out the commands.

[Test Case]
1. Boot up Dell AIO system with v6.5 kernel.
2. Check dmesg and make sure there is no soft lockup error message in it.

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

[Other Info]
dell-uart-backlight is still a Ubuntu only driver, so submit the patch
as UBUNTU: SAUCE: patch.

Chia-Lin Kao (AceLan) (1):
  UBUNTU: SAUCE: platform/x86: dell-uart-backlight: replace
    chars_in_buffer() with flush_chars()

 drivers/platform/x86/dell/dell-uart-backlight.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

-- 
2.34.1