2023-10-23 07:49:22

by Tony Lindgren

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

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 <[email protected]>
Cc: Bruce Ashfield <[email protected]>
Cc: Mikko Rapeli <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Randy MacLeod <[email protected]>
Signed-off-by: Tony Lindgren <[email protected]>
---
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;
}
--
2.42.0

2023-10-23 09:41:37

by Richard Purdie

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

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 <[email protected]>

Tested-by: Richard Purdie <[email protected]>

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 <[email protected]>
> Cc: Mikko Rapeli <[email protected]>
> Cc: Paul Gortmaker <[email protected]>
> Cc: Randy MacLeod <[email protected]>
> Signed-off-by: Tony Lindgren <[email protected]>
> ---
> 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;
> }