Re: [PATCH] serial: core: Fix runtime PM handling for pending tx

[Richard Purdie]

On Mon, 2023-10-23 at 10:48 +0300, Tony Lindgren wrote:
> Richard reported that a serial port may end up sometimes with tx data
> pending in the buffer for long periods of time.
> 
> Turns out we bail out early on any errors from pm_runtime_get(),
> including -EINPROGRESS. To fix the issue, we need to ignore -EINPROGRESS
> as we only care about the runtime PM usage count at this point. We check
> for an active runtime PM state later on for tx.
> 
> Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM")
> Reported-by: Richard Purdie <richard.purdie@xxxxxxxxxxxxxxxxxxx>

Tested-by: Richard Purdie <richard.purdie@xxxxxxxxxxxxxxxxxxx>

Thanks, I can confirm that since we added this into our builds/tests
we've not seen the serial data go missing.

Cheers,

Richard

> Cc: Bruce Ashfield <bruce.ashfield@xxxxxxxxx>
> Cc: Mikko Rapeli <mikko.rapeli@xxxxxxxxxx>
> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> Cc: Randy MacLeod <randy.macleod@xxxxxxxxxxxxx>
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
>  drivers/tty/serial/serial_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -146,7 +146,7 @@ static void __uart_start(struct uart_state *state)
>  
>  	/* Increment the runtime PM usage count for the active check below */
>  	err = pm_runtime_get(&port_dev->dev);
> -	if (err < 0) {
> +	if (err < 0 && err != -EINPROGRESS) {
>  		pm_runtime_put_noidle(&port_dev->dev);
>  		return;
>  	}