Re: [RFC PATCH 6/7] serial: General support for multipoint addresses

[Ilpo Järvinen]

On Wed, 9 Mar 2022, Lukas Wunner wrote:

> On Mon, Mar 07, 2022 at 11:48:01AM +0200, Ilpo Järvinen wrote:
> > On Sun, 6 Mar 2022, Lukas Wunner wrote:
> > > On Wed, Mar 02, 2022 at 11:56:05AM +0200, Ilpo Järvinen wrote:
> > > > This change is necessary for supporting devices with RS485
> > > > multipoint addressing [*].
> > > 
> > > If this is only used with RS485, why can't we just store the
> > > addresses in struct serial_rs485 and use the existing TIOCSRS485
> > > and TIOCGRS485 ioctls?  There's 20 bytes of padding left in
> > > struct serial_rs485 which you could use.  No need to add more
> > > user-space ABI.
> > 
> > It could if it is agreed that serial multipoint addressing is just
> > a thing in RS-485 and nowhere else? In that case, there is no point
> > in adding more generic support for it.
> 
> It's just that the above-quoted sentence in the commit message
> specifically mentions RS485.

That sentence is just to justify why addressing mode is needed,
not to take a stance on whether it is only used with RS485 or not.

> If you intend to use it with RS232
> as well, that should be made explicit, otherwise one wonders why
> it wasn't integrated into struct serial_rs485.
> 
> I have no idea how common 9th bit addressing mode is with RS232.
> Goggle turns up links saying it's mainly used with RS485, "but also
> RS232".  Since RS232 isn't a bus but a point-to-point link,
> 9th bit addressing doesn't seem to make as much sense.

While I don't know any better, I can image though that with an 
RS232-to-RS485 converter, it could make some sense.

If I put them back to serial_rs485 / rs485 config, it's basically just 
where I initially started from with this patchset (offlist).


-- 
 i.