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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Aug 19, 2026 at 08:31:10AM +0100, Lucas Tanure wrote:
> On 19/08/2026 07:49, Greg Kroah-Hartman wrote:
> > On Wed, Aug 19, 2026 at 07:40:17AM +0100, Lucas Tanure wrote:
> > > On 19/08/2026 06:57, Greg Kroah-Hartman wrote:
> > > > 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.
> > > > 
> > > Hi,
> > > 
> > > Understood. I thought preventing 8250 from probing on devices that don't use
> > > it would be a good idea, and fix my bug. Thanks for the feedback.
> > > 
> > > I will tak to Amlogic list the ttyS name collision introduced for the new
> > > Amlogic SoCs in e71aab9d6132.
> > 
> > That was an explicit decision by Amlogic to do that, so there should not
> > be any collisions as their systems should NOT be having the older 8250
> > device tree entries.
> > 
> > So perhaps just fix your device tree to not be broken?
> > 
> > thanks,
> > 
> > greg k-h
> Hi,
> 
> There are no 8250 nodes in the Vim4 device tree.
> At __serial8250_isa_init_ports() in 8250_platform.c it creates nr_uarts
> ports unconditionally:
> 
>       for (i = 0; i < nr_uarts; i++)
>               serial8250_setup_port(i);

Then the amlogic driver should not be attempting to use the same device
nodes.  Something is broken somewhere, and I don't think it is in the
30+ year old isa code :)

thanks,

greg k-h