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. > > [*] Technically, RS485 is just an electronic spec and does not > > itself specify the 9th bit addressing mode but 9th bit seems > > at least "semi-standard" way to do addressing with RS485. > > Is 9th bit addressing actually used by an Intel customer or was > it implemented just for feature completeness? I think this mode > isn't used often (I've never seen a use case myself), primarily > because it requires disabling parity. On what basis? ...The datasheet I'm looking at has a timing diagram with both D8 (9th bit) and parity so I think your information must be incorrect. I don't have direct contacts with customers but I'm told it's important for other org's customers. -- i.
