Hi, Am Donnerstag, 19. März 2020, 06:40:34 CET schrieb Lukas Wunner: > On Wed, Mar 18, 2020 at 07:49:08PM +0100, Heiko Stübner wrote: > > Looking at tty-next I notice that you're right. When I started working > > on this I only found the stuff from 2018 I linked to but didn't imagine > > that in that exact moment someone else would also work on that area. > > There are some more patches in the pipeline for the next cycle > to add support for an rs485 bus termination GPIO. They're on > the tip of this branch: > > https://github.com/RevolutionPi/linux/commits/revpi-4.19 > > Just so you know in advance and duplicate work is avoided. do you plan on submitting these soonish? Because looking at your termination-gpio change makes me want to do something similar for my RE-gpio ... instead of trying to mangle this into the DTR thingy. > > > The DTR-for-RE thing seems a bit nonstandard, I'm not sure if this is > > > eligible for mainline or if it's something that should be kept in your > > > downstream tree. But no harm in submitting it to the list. > > > > I'm fine either way - maybe I also get a pointer on what may be a better > > approach ;-) > > > > At least DTR as "Data Terminal Ready" did sound somewhat matching for > > the "Receive Enable" of RS485 (and it's also the only other output pin > > in the mctrl gpio list). > > Some UARTs allow disabling the receiver, this can be taken advantage of > to implement half-duplex mode. It's what I did in 8250_bcm2835aux.c. > > On the Revolution Pi devices, !RE is usually connected to ground, so > reception is always enabled and it cannot be disabled in software > except by turning off the UART receiver. > > There are also boards out there which connect !RE to RTS. Then only > half-duplex mode is supported by the hardware and there's no way for > software to work around it. yep and on our board we have DE and RE on separate gpios, so I guess it makes sense to use that pin how it was intended ;-) . So I guess having that as rs485-re-gpios property might be the best way. Heiko
