| Message ID | 20200517215610.2131618-1-heiko@sntech.de |
|---|---|
| Headers | show |
| Series | serial: 8250: Add rs485 emulation to 8250_dw | expand |
Hi, On 17.05.20 23:56, Heiko Stuebner wrote: > From: Heiko Stuebner<heiko.stuebner@theobroma-systems.com> > > 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. > > Signed-off-by: Heiko Stuebner<heiko.stuebner@theobroma-systems.com> > --- > drivers/tty/serial/8250/8250_port.c | 7 ++++++- > drivers/tty/serial/serial_core.c | 10 ++++++++++ > include/linux/serial_core.h | 1 + > 3 files changed, 17 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > index 6975bd3ecb7d..9e8fec85d1a3 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -1444,6 +1444,7 @@ static void serial8250_stop_rx(struct uart_port *port) > void serial8250_em485_stop_tx(struct uart_8250_port *p) > { > unsigned char mcr = serial8250_in_MCR(p); > + struct uart_port *port = &p->port; > > if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND) > mcr |= UART_MCR_RTS; > @@ -1457,6 +1458,7 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p) > * Enable previously disabled RX interrupts. > */ > if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) { > + gpiod_set_value(port->rs485_re_gpio, 1); > serial8250_clear_and_reinit_fifos(p); > > p->ier |= UART_IER_RLSI | UART_IER_RDI; > @@ -1597,9 +1599,12 @@ static inline void __start_tx(struct uart_port *port) > void serial8250_em485_start_tx(struct uart_8250_port *up) > { > unsigned char mcr = serial8250_in_MCR(up); > + struct uart_port *port = &up->port; > > - if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX)) > + if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX)) { > + gpiod_set_value(port->rs485_re_gpio, 0); > serial8250_stop_rx(&up->port); > + } > > if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND) > mcr |= UART_MCR_RTS; > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index 15ad8737b72b..c0d3ab32b49a 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -3149,6 +3149,16 @@ int uart_get_rs485_mode(struct uart_port *port) > return ret; > } > > + port->rs485_re_gpio = devm_gpiod_get_optional(dev, "rs485-rx-enable", > + GPIOD_OUT_HIGH); The half duplex emulation can be disabled on-boot or later-on using ioctls in systems that can switch between half and full duplex modes. In that case this gpio should probably be released as it can probably prevent enabling the transceiver-sender mode. I suggest we set the gpio to output active in the em485_init callback and stop driving it in the em485_destroy callback. Regards > + if (IS_ERR(port->rs485_re_gpio)) { > + ret = PTR_ERR(port->rs485_re_gpio); > + port->rs485_re_gpio = NULL; > + if (ret != -EPROBE_DEFER) > + dev_err(dev, "Cannot get rs485-rx-enable-gpios\n"); > + return ret; > + } > + > return 0; > } > EXPORT_SYMBOL_GPL(uart_get_rs485_mode); > diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h > index 108f95411471..dfe18ddb1674 100644 > --- a/include/linux/serial_core.h > +++ b/include/linux/serial_core.h > @@ -253,6 +253,7 @@ struct uart_port { > const struct attribute_group **tty_groups; /* all attributes (serial core use only) */ > struct serial_rs485 rs485; > struct gpio_desc *rs485_term_gpio; /* enable RS485 bus termination */ > + struct gpio_desc *rs485_re_gpio; /* gpio RS485 receive enable */ > struct serial_iso7816 iso7816; > void *private_data; /* generic platform data pointer */ > };
This series tries to revive the work of Giulio Benetti from 2018 [0] which seemed to have stalled at that time. The board I needed that on also had the additional caveat that it uses non-standard pins for DE/RE so needed gpio mctrl layer as well and even more special needed to control the RE pin manually not as part of it being connected to the DE signal as seems to be the standard. Depends on Lukas Wunner's series adding the rs485 bus term gpio: https://lore.kernel.org/r/cover.1588505407.git.lukas@wunner.de changes in v3: - wording fixes for dt-binding (Andy) - maxItems 1 in dt-binding (Lukas) - use devm_gpiod_get_optional (Andy) - remove unneeded gpio checks (Andy) - use GPIOD_OUT_HIGH for initial value (Lukas) - split loop-reading into the existing timer infrastructure Changes in v2: - move to recent rs485 improvements in tty-next - added a capability for TEMT interrupt presence - external gpio for optional receiver-enable handling - timeout polling via the generic readx_poll_timeout Changes from the 2018 submission include: - add timeout when waiting for fifos to clear using a new helper - move on-boot enablement of the rs485 mode to after registering the port. This saves having to copy the em485 struct as done originally, which also ran into spinlock-debug warnings when testing and also makes it actually possible to use the mctrl gpio layer for non-standard gpios. Giulio Benetti (2): serial: 8250: Handle implementations not having TEMT interrupt using em485 serial: 8250_dw: add em485 support Heiko Stuebner (3): serial: 8520_port: Fix function param documentation dt-bindings: serial: Add binding for rs485 receiver enable GPIO serial: 8250: Support separate rs485 rx-enable GPIO .../devicetree/bindings/serial/rs485.yaml | 4 ++ drivers/tty/serial/8250/8250.h | 1 + drivers/tty/serial/8250/8250_bcm2835aux.c | 2 +- drivers/tty/serial/8250/8250_dw.c | 3 + drivers/tty/serial/8250/8250_of.c | 2 + drivers/tty/serial/8250/8250_omap.c | 2 +- drivers/tty/serial/8250/8250_port.c | 60 ++++++++++++++++--- drivers/tty/serial/serial_core.c | 10 ++++ include/linux/serial_core.h | 1 + 9 files changed, 76 insertions(+), 9 deletions(-)