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SubjectRe: [PATCH 1/2] serial: imx: Add rs485 support to imx thanks to rs485 functions in serial_core
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Hello,

On Wednesday 11 February 2015 16:30:34, Aurelien BOUIN wrote:
> This is a patch to add rs485 support with imx freescale processor
> It allows to set the transmit pin used in the structure padding (rs485.padding[0])

Nice idea to use the padding for GPIO configuration. I've done an implementation using board-specific call-backs which doesn't work with DT.

> Signed-off-by: Aurelien BOUIN <a.bouin@gmail.com>
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 4c5e909..a086eef 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -53,6 +53,8 @@
> #include <asm/irq.h>
> #include <linux/platform_data/serial-imx.h>
> #include <linux/platform_data/dma-imx.h>
> +#include <linux/uaccess.h>
> +#include <linux/gpio.h>
>
> /* Register definitions */
> #define URXD0 0x0 /* Receiver Register */
> @@ -280,6 +282,56 @@ static struct of_device_id imx_uart_dt_ids[] = {
> };
> MODULE_DEVICE_TABLE(of, imx_uart_dt_ids);
>
> +static inline struct imx_port *to_imx_port(struct uart_port *uart)
> +{
> + return container_of(uart, struct imx_port, port);
> +}
> +
> +static void imx_rs485_stop_tx(struct imx_port *imx_uart_port)
> +{
> + /*
> + * Deactivate transmit pin configured in the structure padding
> + */
> + gpio_set_value(imx_uart_port->port.rs485.padding[0], 0);
> +}
> +
> +static void imx_rs485_start_tx(struct imx_port *imx_uart_port)
> +{
> + /*
> + * Activate transmit pin configured in the structure padding
> + */
> + gpio_set_value(imx_uart_port->port.rs485.padding[0], 1);
> +}

Please add the feature to support active-low GPIOs, e.g. using rs485.padding[1].

> +/* Enable or disable the rs485 support */
> +static int imx_config_rs485(struct uart_port *port,
> + struct serial_rs485 *rs485conf)
> +{
> + port->rs485 = *rs485conf;
> + if (rs485conf->flags & SER_RS485_ENABLED) {
> + int ret;
> +
> + dev_dbg(port->dev, "Setting UART /dev/ttymxc%d with the pin 0x%x to RS485\n",
> + port->line, port->rs485.padding[0]);
> + /*
> + * Set the transmit pin configured in the structure padding
> + * in GPIO output
> + */
> + ret = gpio_request(port->rs485.padding[0], "RS485 transmit");
> + if (ret)
> + dev_err(port->dev, "Unable to request the RS485 transmit %d\n",
> + port->rs485.padding[0]);
> + gpio_direction_output(port->rs485.padding[0], 0);
> +
> + } else {
> + dev_dbg(port->dev, "Setting UART /dev/ttymxc%d to RS232\n",
> + port->line);
> + if (port->rs485.padding[0])
> + gpio_free(port->rs485.padding[0]);
> + }
> + return 0;
> +}
> +
> static inline unsigned uts_reg(struct imx_port *sport)
> {
> return sport->devdata->uts_reg;
> @@ -580,6 +632,15 @@ static void imx_start_tx(struct uart_port *port)
> struct imx_port *sport = (struct imx_port *)port;
> unsigned long temp;
>
> + if (port->rs485.flags & SER_RS485_ENABLED) {
> + imx_rs485_start_tx(sport);
> + /*
> + * Transmit complete interrupt change to receiver mode
> + */
> + temp = readl(sport->port.membase + UCR4);
> + writel(temp | UCR4_TCEN, sport->port.membase + UCR4);
> + }
> +

If you run a RT-PREEMPT kernel, interrupts aren't actually disabled here. So when you enable the TXDC interrupt here, it will fire up immediately.
Move that after calling imx_transmit_buffer so you are sure there are actually characters inserted.

> if (USE_IRDA(sport)) {
> /* half duplex in IrDA mode; have to disable receive mode */
> temp = readl(sport->port.membase + UCR4);
> @@ -693,8 +754,10 @@ static irqreturn_t imx_rxint(int irq, void *dev_id)
> goto out;
> continue;
> }
> -
> - rx &= sport->port.read_status_mask;
> + /*
> + * Preserve characters with parity or framing errors
> + */
> + rx &= sport->port.read_status_mask | 0xFF;
>
> if (rx & URXD_BRK)
> flg = TTY_BREAK;
> @@ -747,8 +810,30 @@ static irqreturn_t imx_int(int irq, void *dev_id)
> struct imx_port *sport = dev_id;
> unsigned int sts;
> unsigned int sts2;
> + unsigned int cr1, cr2, cr3, cr4;
>
> sts = readl(sport->port.membase + USR1);
> + sts2 = readl(sport->port.membase + USR2);
> + cr1 = readl(sport->port.membase + UCR1);
> + cr2 = readl(sport->port.membase + UCR2);
> + cr3 = readl(sport->port.membase + UCR3);
> + cr4 = readl(sport->port.membase + UCR4);
> +
> + if (sport->port.rs485.flags & SER_RS485_ENABLED) {
> + /*
> + * Check if the transmit is complete
> + */
> + if ((cr4 & UCR4_TCEN) && (sts2 & USR2_TXDC)) {

Can this actually happen that UCR4_TCEN is unset when in S485 mode?

Best regards,
Alexander
--
Dipl.-Inf. Alexander Stein

SYS TEC electronic GmbH
Am Windrad 2
08468 Heinsdorfergrund
Tel.: 03765 38600-1156
Fax: 03765 38600-4100
Email: alexander.stein@systec-electronic.com
Website: www.systec-electronic.com

Managing Director: Dipl.-Phys. Siegmar Schmidt
Commercial registry: Amtsgericht Chemnitz, HRB 28082



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