[PATCH v14 1/1] tty: serial: Add Nuvoton ma35d1 serial driver support

[Arnd Bergmann]

On Thu, Jun 15, 2023, at 17:00, Greg Kroah-Hartman wrote:
> On Thu, Jun 15, 2023 at 04:01:55PM +0200, Arnd Bergmann wrote:
>> Since the number is exported to userspace in serial_struct,
>> it might be better to pick a new constant such as
>> 
>> #define PORT_SERIAL_GENERIC (-1)
>> 
>> in order to be less ambiguous. It's a signed integer, so -1
>> would work here this would clearly be a special value, or
>> another option might be to use 255 as something that is
>> slightly less special but still recognizable as something
>> that may have a special meaning.
>
> A new constant would be good, 255 is nice, and then we can move everyone
> to use it unless they can specifically show a reason why it will not
> work for them.
>
> I think originally this was used to do device-specific ioctls, right?
> That shouldn't be happening anymore, hopefully...

The only thing I could find is that you can use TIOCSSERIAL to set
the type between the supported types within a driver, which changes
the behavior in some cases, e.g. the exact size and layout of the
register file or its capabilities.

We may need a proper audit of TIOCSSERIAL anyway, I suspect there
are worse things you can do with other settings.

       Arnd