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

[Andrea Righi]

On Tue, Aug 22, 2023 at 11:57:40AM +0800, AceLan Kao wrote:
> 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>

Is there an upstream thread for this? If so it would be nice to add a
link, reference, or a "cherry picked from" line with the URL of the
upstream mail thread.

Thanks,
-Andrea

> ---
>  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
> 
> 
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