Re: [STLinux Kernel] [PATCH 2/8] serial: st-asc: Provide RTS functionality

Peter Griffin
2017-01-25T11:03:57Z

On Tue, 24 Jan 2017, Lee Jones wrote:

> Until this point, it has not been possible for userland serial
> applications (e.g. stty) to toggle the UART RTS line. This can
> be useful with certain configurations. For example, when using
> a Mezzanine on a Linaro 96board, RTS line is used to take the
> on-board microcontroller in and out of reset.
>
> Signed-off-by: Lee Jones <lee.jones@linaro.org>

Acked-by: Peter Griffin <peter.griffin@linaro.org>

> ---
> drivers/tty/serial/st-asc.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
> index 69e6232..397df50 100644
> --- a/drivers/tty/serial/st-asc.c
> +++ b/drivers/tty/serial/st-asc.c
> @@ -30,6 +30,7 @@
> #include <linux/of_platform.h>
> #include <linux/serial_core.h>
> #include <linux/clk.h>
> +#include <linux/gpio/consumer.h>
>
> #define DRIVER_NAME "st-asc"
> #define ASC_SERIAL_NAME "ttyAS"
> @@ -38,6 +39,7 @@
>
> struct asc_port {
> struct uart_port port;
> + struct gpio_desc *rts;
> struct clk *clk;
> unsigned int hw_flow_control:1;
> unsigned int force_m1:1;
> @@ -391,12 +393,27 @@ static unsigned int asc_tx_empty(struct uart_port *port)
>
> static void asc_set_mctrl(struct uart_port *port, unsigned int mctrl)
> {
> + struct asc_port *ascport = to_asc_port(port);
> +
> /*
> - * This routine is used for seting signals of: DTR, DCD, CTS/RTS
> - * We use ASC's hardware for CTS/RTS, so don't need any for that.
> - * Some boards have DTR and DCD implemented using PIO pins,
> - * code to do this should be hooked in here.
> + * This routine is used for seting signals of: DTR, DCD, CTS and RTS.
> + * We use ASC's hardware for CTS/RTS when hardware flow-control is
> + * enabled, however if the RTS line is required for another purpose,
> + * commonly controlled using HUP from userspace, then we need to toggle
> + * it manually, using GPIO.
> + *
> + * Some boards also have DTR and DCD implemented using PIO pins, code to
> + * do this should be hooked in here.
> */
> +
> + if (!ascport->rts)
> + return;
> +
> + /* If HW flow-control is enabled, we can't fiddle with the RTS line */
> + if (asc_in(port, ASC_CTL) & ASC_CTL_CTSENABLE)
> + return;
> +
> + gpiod_set_value(ascport->rts, mctrl & TIOCM_RTS);
> }
>
> static unsigned int asc_get_mctrl(struct uart_port *port)
> @@ -726,6 +743,8 @@ static struct asc_port *asc_of_get_asc_port(struct platform_device *pdev)
> "st,hw-flow-control");
> asc_ports[id].force_m1 = of_property_read_bool(np, "st,force_m1");
> asc_ports[id].port.line = id;
> + asc_ports[id].rts = NULL;
> +
> return &asc_ports[id];
> }
>