Re: [PATCH] serial: qcom-geni: power the console back up on system resume

[Praveen Talari <praveen.talari@oss.qualcomm.com>]

Hi David,

On 18-09-2026 03:44, David Heidelberg via B4 Relay wrote:
> From: David Heidelberg <david@ixit.cz>
>
> The console holds a runtime PM reference on its port, which keeps the
> port powered while the tty is closed. On system suspend
> pm_runtime_force_suspend() powers the port down regardless, but a single
> reference makes pm_runtime_need_not_resume() report the port as not in
> use, so it is marked runtime suspended instead of being flagged for
> pm_runtime_force_resume(). On system resume the port therefore stays
> powered down while uart_resume_port() goes on to program the termios
> settings and re-enable the console.
>
> If the tty has been opened before, uart_resume_port() ends up in
> startup(), whose runtime PM reference powers the port up again, and only
> the register writes made before that are lost. If the tty has never been
> opened (no getty on the port, /dev/console backed by another console),
> nothing powers the port back up and the console stays dead after the
> first suspend.
>
> Resume the port explicitly before uart_resume_port() when the console
> was force suspended.
Thanks for tracking this down. I'm trying to understand the resume flow 
here.

In qcom_geni_serial_resume(), when console_suspend_enabled is set,
we already call pm_runtime_force_resume(dev); before reaching
uart_resume_port().

Given that, could you clarify why an additional:pm_runtime_resume(dev);
is required for the console case?

Specifically, is pm_runtime_force_resume() leaving the device in a
runtime-suspended state despite restoring it from system suspend, or
is there some interaction with the console's runtime PM reference count
that prevents the port from being resumed before uart_resume_port() accesses
the registers?

A bit more detail on why pm_runtime_force_resume() alone is insufficient

would help understand the root cause.


Thanks,

Praveen Talari

>
> Assisted-by: LLM
> Fixes: aee1f94dab13 ("serial: qcom-geni: remove .pm callback, use runtime PM in startup/shutdown")
> Signed-off-by: David Heidelberg <david@ixit.cz>
> ---
>   drivers/tty/serial/qcom_geni_serial.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index a180a00c9e23d..0c9164a1fccda 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -2100,16 +2100,22 @@ static int qcom_geni_serial_resume(struct device *dev)
>   	struct qcom_geni_private_data *private_data = uport->private_data;
>   
>   	if (console_suspend_enabled || !uart_console(uport)) {
>   		ret = pm_runtime_force_resume(dev);
>   		if (ret)
>   			return ret;
>   	}
>   
> +	if (console_suspend_enabled && uart_console(uport)) {
> +		ret = pm_runtime_resume(dev);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
>   	ret = uart_resume_port(private_data->drv, uport);
>   	if (uart_console(uport)) {
>   		geni_icc_set_tag(&port->se, QCOM_ICC_TAG_ALWAYS);
>   		geni_icc_set_bw(&port->se);
>   	}
>   	return ret;
>   }
>   
>
> ---
> base-commit: 3d83758432b5e6ed9507500a57efb0f3af41ee7d
> change-id: 20260918-qcom-geni-pm-e0ff5899c948
> prerequisite-change-id: 20260828-serial-qcom-geni-fix-unbalanced-rpm-resume-814e630326b9:v1
> prerequisite-patch-id: a2666a59a68190a3f438cec8aa167111c21dc8ca
>
> Best regards,
> --
> David Heidelberg <david@ixit.cz>
>
>