On Mon, May 18, 2020 at 06:13:16PM +0200, Maarten Brock wrote: > On 2020-05-18 17:22, Lukas Wunner wrote: > > On Mon, May 18, 2020 at 06:12:41PM +0300, Andy Shevchenko wrote: > > > On Sun, May 17, 2020 at 11:56:08PM +0200, Heiko Stuebner wrote: > > > > From: Heiko Stuebner <heiko.stuebner@xxxxxxxxxxxxxxxxxxxxx> > > > > > > > > The RE signal is used to control the duplex mode of transmissions, > > > > aka receiving data while sending in full duplex mode, while stopping > > > > receiving data in half-duplex mode. > > > > > > > > On a number of boards the !RE signal is tied to ground so reception > > > > is always enabled except if the UART allows disabling the receiver. > > > > This can be taken advantage of to implement half-duplex mode - like > > > > done on 8250_bcm2835aux. > > > > > > > > Another solution is to tie !RE to RTS always forcing half-duplex mode. > > > > > > > > And finally there is the option to control the RE signal separately, > > > > like done here by introducing a new rs485-specific gpio that can be > > > > set depending on the RX_DURING_TX setting in the common em485 callbacks. > > > > > > ... > > > > > > > + port->rs485_re_gpio = devm_gpiod_get_optional(dev, "rs485-rx-enable", > > > > + GPIOD_OUT_HIGH); > > > > > > While reviewing some other patch I realized that people are missing > > > the > > > point of these GPIO flags when pin is declared to be output. > > > > > > HIGH here means "asserted" (consider active-high vs. active-low in > > > general). Is that the intention here? > > > > > > Lukas, same question to your patch. > > > > Yes. "High", i.e. asserted, means "termination enabled" in the case of > > my patch and "receiver enabled" in the case of Heiko's patch. > > But "High" on a gpio would disable the receiver when connected to !RE. No, that's exactly the point of the terminology (asserted means active whatever polarity it is). You need to define active-low in GPIO description. -- With Best Regards, Andy Shevchenko
