[PATCH] serial: 8250: don't register ports that have no hardware

[PATCH] serial: 8250: don't register ports that have no hardware

[Lucas Tanure]

The 8250 driver creates a fixed set of port slots at boot and
registers a ttyS device for each one, even when the slot describes no
hardware. On device tree platforms those slots are empty, but they
still take the ttyS0..ttyS3 names.

New Amlogic SoCs (S4, T7) name their real UARTs ttyS as well. With
both drivers built in, as in arm64 defconfig, the real port fails to bind:

  sysfs: cannot create duplicate filename '/class/tty/ttyS0'
  meson_uart fe078000.serial: Cannot register tty device on line 0

Skip slots that have no I/O and no memory address. Legacy x86 slots
come with resources and are not affected.

Signed-off-by: Lucas Tanure <tanure@linux.com>
Assisted-by: Claude:claude-fable-5
---
 drivers/tty/serial/8250/8250_core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index f49862d90eeb..e66e0cdbb210 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -378,6 +378,14 @@ void __init serial8250_register_ports(struct uart_driver *drv, struct device *de
 		if (up->port.dev)
 			continue;
 
+		/*
+		 * Skip slots that describe no hardware: they would only
+		 * take up ttyS<n> names. Real ports get their node when
+		 * they claim a slot in serial8250_register_8250_port().
+		 */
+		if (!up->port.iobase && !up->port.mapbase && !up->port.membase)
+			continue;
+
 		up->port.dev = dev;
 
 		if (uart_console_registered(&up->port))
-- 
2.55.0

Re: [PATCH] serial: 8250: don't register ports that have no hardware

[Jiri Slaby]

On 18. 08. 26, 20:52, Lucas Tanure wrote:
> The 8250 driver creates a fixed set of port slots at boot and
> registers a ttyS device for each one, even when the slot describes no
> hardware. On device tree platforms those slots are empty, but they
> still take the ttyS0..ttyS3 names.
> 
> New Amlogic SoCs (S4, T7) name their real UARTs ttyS as well. With
> both drivers built in, as in arm64 defconfig, the real port fails to bind:
> 
>    sysfs: cannot create duplicate filename '/class/tty/ttyS0'
>    meson_uart fe078000.serial: Cannot register tty device on line 0
> 
> Skip slots that have no I/O and no memory address. Legacy x86 slots
> come with resources and are not affected.
> 
> Signed-off-by: Lucas Tanure <tanure@linux.com>
> Assisted-by: Claude:claude-fable-5
> ---
>   drivers/tty/serial/8250/8250_core.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index f49862d90eeb..e66e0cdbb210 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -378,6 +378,14 @@ void __init serial8250_register_ports(struct uart_driver *drv, struct device *de
>   		if (up->port.dev)
>   			continue;
>   
> +		/*
> +		 * Skip slots that describe no hardware: they would only
> +		 * take up ttyS<n> names. Real ports get their node when
> +		 * they claim a slot in serial8250_register_8250_port().
> +		 */
> +		if (!up->port.iobase && !up->port.mapbase && !up->port.membase)
> +			continue;

So you can no longer set up those ports via TIOCSSERIAL?

And what about already registered consoles?

Why does meson register ttyS* in the first place?

F*ck AI proposed changes.

thanks,
-- 
js
suse labs

Re: [PATCH] serial: 8250: don't register ports that have no hardware

[Greg Kroah-Hartman]

On Tue, Aug 18, 2026 at 07:52:00PM +0100, Lucas Tanure wrote:
> The 8250 driver creates a fixed set of port slots at boot and
> registers a ttyS device for each one, even when the slot describes no
> hardware. On device tree platforms those slots are empty, but they
> still take the ttyS0..ttyS3 names.
> 
> New Amlogic SoCs (S4, T7) name their real UARTs ttyS as well. With
> both drivers built in, as in arm64 defconfig, the real port fails to bind:

Then fix that bug, don't break everyone else's systems because of it.

greg k-h