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SubjectRe: [PATCH] serial: 8250: add option to disable registration of legacy ISA ports
Greg Kroah-Hartman <> writes:

> On Thu, Jan 28, 2021 at 05:22:44PM +0000, Mans Rullgard wrote:
>> On systems that do not have the traditional PC ISA serial ports, the
>> 8250 driver still creates non-functional device nodes. This change
>> makes only ports that actually exist (PCI, DT, ...) get device nodes.
>> Signed-off-by: Mans Rullgard <>
>> ---
>> drivers/tty/serial/8250/8250_core.c | 26 ++++++++++++++++++++------
>> drivers/tty/serial/8250/Kconfig | 5 +++++
>> 2 files changed, 25 insertions(+), 6 deletions(-)
>> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
>> index cae61d1ebec5..49695dd3677c 100644
>> --- a/drivers/tty/serial/8250/8250_core.c
>> +++ b/drivers/tty/serial/8250/8250_core.c
>> @@ -555,6 +555,7 @@ static void __init serial8250_isa_init_ports(void)
>> }
>> }
>> +#ifdef CONFIG_SERIAL_8250_ISA
> This is just making a mess of the code.

It was already a mess.

> To do this right, pull the isa code out into a separate file and put
> the #ifdef in a .h file, so we can properly maintain and support this
> code over time. This change as-is is not going to make that any
> easier :(

I might put in that effort if there's a reasonable chance this change
will be accepted. If it's going to be rejected regardless, I'd rather
not waste my time.

>> +config SERIAL_8250_ISA
>> + bool "8250/16550 ISA device support" if EXPERT
> So, no one will set this?

I followed the pattern of the existing SERIAL_8250_PNP option. Was that
a mistake? How would you prefer it?

> What userspace visable change will be caused by this?

There won't be /dev/ttyS devices for ports that don't exist.

> Will ports get renumbered?

Not if they had predictable numbers to begin with.

> What harm is this causing systems today without this change?

It means I have to somehow maintain a separate list of which ports are
real and which should be ignored, or else try to distinguish real errors
from those caused by trying to access the bogus ports.

Måns Rullgård

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