On Tue, Sep 21, 2021 at 01:33:44PM +0300, Tony Lindgren wrote:
> We can use the prep_tx() call to wake up an idle serial port. This allows
> ust to remove the depedency to pm_runtime_irq_safe() for 8250_omap driver
> in the following patches.
>
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_port.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1650,6 +1650,29 @@ static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t)
> return HRTIMER_NORESTART;
> }
>
> +static int serial8250_prep_tx(struct uart_port *port)
> +{
> + struct uart_8250_port *up = up_to_u8250p(port);
> + struct device *dev = up->port.dev;
> + int err;
> +
> + if (!(up->capabilities & UART_CAP_RPM))
> + return 0;
> +
> + if (!pm_runtime_suspended(dev)) {
> + pm_runtime_mark_last_busy(dev);
> + return 0;
> + }
> +
> + err = pm_request_resume(dev);
> + if (err < 0) {
> + dev_warn(dev, "prep_tx wakeup failed: %d\n", err);
> + return err;
> + }
How is this supposed to work without a runtime PM usage-counter
increment? What's to prevent the port from suspending again while it's
transmitting?
> +
> + return -EINPROGRESS;
> +}
Johan
