[PATCH] serial: 8250: Add Armada 38x earlycon support

[PATCH] serial: 8250: Add Armada 38x earlycon support

[Rosen Penev]

Register the Armada 38x UART compatible with the built-in 8250
earlycon implementation so stdout-path can enable an early console
without adding a generic ns16550a compatible to the device tree.

Keeping the vendor-specific compatible avoids exposing the UART to the
generic OF 8250 runtime driver while preserving the DesignWare driver
Armada-specific runtime handling.

Assisted-by: Codex:GPT-5
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/tty/serial/8250/8250_early.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index 44ec209f37c4..265d49850e15 100644
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -175,6 +175,7 @@ EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 EARLYCON_DECLARE(uart, early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
+OF_EARLYCON_DECLARE(uart, "marvell,armada-38x-uart", early_serial8250_setup);
 OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
 OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
 
-- 
2.55.0

Re: [PATCH] serial: 8250: Add Armada 38x earlycon support

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Runtime PM circular dependency during port registration in `dw8250_probe()`.
--

commit b5bac3793a0a37f84d80f37cd62c9577811449ef
Author: Rosen Penev <rosenp@gmail.com>

serial: 8250: Add Armada 38x earlycon support

This commit registers the Armada 38x UART compatible with the built-in 8250
earlycon implementation. This allows stdout-path to enable an early console
while preserving the vendor-specific compatible to retain DesignWare driver
runtime handling.

> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
> index 44ec209f37c47..265d49850e150 100644
> --- a/drivers/tty/serial/8250/8250_early.c
> +++ b/drivers/tty/serial/8250/8250_early.c
> @@ -175,6 +175,7 @@ EARLYCON_DECLARE(uart8250, early_serial8250_setup);
>  EARLYCON_DECLARE(uart, early_serial8250_setup);
>  OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
>  OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
> +OF_EARLYCON_DECLARE(uart, "marvell,armada-38x-uart", early_serial8250_setup);

[Severity: High]
This is a pre-existing issue, but since this patch relies on preserving the
DesignWare driver's runtime handling, could the current runtime PM logic
cause a circular dependency during port registration?

Looking at dw8250_probe() in drivers/tty/serial/8250/8250_dw.c, port
registration happens before runtime PM is enabled:

drivers/tty/serial/8250/8250_dw.c:dw8250_probe() {
	...
	data->data.line = serial8250_register_8250_port(up);
	if (data->data.line < 0)
		return data->data.line;

	platform_set_drvdata(pdev, data);

	pm_runtime_enable(dev);
	...
}

The registration call eventually reaches uart_add_one_port(), which
synchronously invokes the pm callback dw8250_do_pm(). This callback
attempts to use runtime PM APIs:

drivers/tty/serial/8250/8250_dw.c:dw8250_do_pm() {
	if (!state)
		pm_runtime_get_sync(port->dev);

	serial8250_do_pm(port, state, old);

	if (state)
		pm_runtime_put_sync_suspend(port->dev);
}

Since pm_runtime_enable() hasn't been called yet when the callback runs,
would pm_runtime_get_sync() operate on an uninitialized device? Does this
sequence risk blocking tasks and hanging worker threads during device probe?

>  OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
>  OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260902221709.340393-1-rosenp@gmail.com?part=1

Re: [PATCH] serial: 8250: Add Armada 38x earlycon support

[Greg Kroah-Hartman]

On Wed, Sep 02, 2026 at 03:17:09PM -0700, Rosen Penev wrote:
> Register the Armada 38x UART compatible with the built-in 8250
> earlycon implementation so stdout-path can enable an early console
> without adding a generic ns16550a compatible to the device tree.
> 
> Keeping the vendor-specific compatible avoids exposing the UART to the
> generic OF 8250 runtime driver while preserving the DesignWare driver
> Armada-specific runtime handling.
> 
> Assisted-by: Codex:GPT-5
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  drivers/tty/serial/8250/8250_early.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
> index 44ec209f37c4..265d49850e15 100644
> --- a/drivers/tty/serial/8250/8250_early.c
> +++ b/drivers/tty/serial/8250/8250_early.c
> @@ -175,6 +175,7 @@ EARLYCON_DECLARE(uart8250, early_serial8250_setup);
>  EARLYCON_DECLARE(uart, early_serial8250_setup);
>  OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
>  OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
> +OF_EARLYCON_DECLARE(uart, "marvell,armada-38x-uart", early_serial8250_setup);
>  OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
>  OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
>  
> -- 
> 2.55.0
> 

How was this tested?

thanks,

greg k-h

Re: [PATCH] serial: 8250: Add Armada 38x earlycon support

[Rosen Penev]

On Wed, Sep 23, 2026 at 5:22 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Wed, Sep 02, 2026 at 03:17:09PM -0700, Rosen Penev wrote:
> > Register the Armada 38x UART compatible with the built-in 8250
> > earlycon implementation so stdout-path can enable an early console
> > without adding a generic ns16550a compatible to the device tree.
> >
> > Keeping the vendor-specific compatible avoids exposing the UART to the
> > generic OF 8250 runtime driver while preserving the DesignWare driver
> > Armada-specific runtime handling.
> >
> > Assisted-by: Codex:GPT-5
> > Signed-off-by: Rosen Penev <rosenp@gmail.com>
> > ---
> >  drivers/tty/serial/8250/8250_early.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
> > index 44ec209f37c4..265d49850e15 100644
> > --- a/drivers/tty/serial/8250/8250_early.c
> > +++ b/drivers/tty/serial/8250/8250_early.c
> > @@ -175,6 +175,7 @@ EARLYCON_DECLARE(uart8250, early_serial8250_setup);
> >  EARLYCON_DECLARE(uart, early_serial8250_setup);
> >  OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
> >  OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
> > +OF_EARLYCON_DECLARE(uart, "marvell,armada-38x-uart", early_serial8250_setup);
> >  OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
> >  OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
> >
> > --
> > 2.55.0
> >
>
> How was this tested?
This is actually a bugfix to avoid having to add "ns16550a" in dts,
which arose from a dt bindings commit asking why "ns16550a" is even
needed.

Anyway, the actual earlycon functionality was probably tested on a
Turris Omnia given the author of 62480772263a
>
> thanks,
>
> greg k-h