Re: [PATCH v5 2/3] tty: Add software emulated RS485 support for 8250

[Andy Shevchenko]

On Sat, Dec 12, 2015 at 1:23 PM, Matwey V. Kornilov <matwey@xxxxxxxxxx> wrote:
> Implementation of software emulation of RS485 direction handling is based
> on omap_serial driver.
> Before and after transmission RTS is set to the appropriate value.
>
> Note that before calling serial8250_em485_init the caller has to
> ensure that UART will interrupt when shift register empty. Otherwise,
> emultaion cannot be used.
>
> Both serial8250_em485_init and serial8250_em485_destroy are
> idempotent functions.

Just nitpick suggesting to rename both struct and field:

struct uart_8250_rs485em *rs485em;

(might be 'sw' suffix as well, which I like more â rs485sw)

and corresponding local variables if any.

>
> Signed-off-by: Matwey V. Kornilov <matwey@xxxxxxxxxx>
> ---
>  drivers/tty/serial/8250/8250.h      |   6 ++
>  drivers/tty/serial/8250/8250_port.c | 161 +++++++++++++++++++++++++++++++++++-
>  include/linux/serial_8250.h         |   7 ++
>  3 files changed, 170 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index d54dcd8..a3816c6 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -117,6 +117,12 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
>  struct uart_8250_port *serial8250_get_port(int line);
>  void serial8250_rpm_get(struct uart_8250_port *p);
>  void serial8250_rpm_put(struct uart_8250_port *p);
> +int serial8250_em485_init(struct uart_8250_port *p);
> +void serial8250_em485_destroy(struct uart_8250_port *p);
> +static inline bool serial8250_em485_enabled(struct uart_8250_port *p)
> +{
> +       return p->rs485_emul && (p->port.rs485.flags & SER_RS485_ENABLED);
> +}
>
>  #if defined(__alpha__) && !defined(CONFIG_PCI)
>  /*
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 8ad0b2d..394d0d2 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -37,6 +37,7 @@
>  #include <linux/slab.h>
>  #include <linux/uaccess.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/timer.h>
>
>  #include <asm/io.h>
>  #include <asm/irq.h>
> @@ -504,6 +505,31 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
>         }
>  }
>
> +static inline void serial8250_em485_rts_on_send(struct uart_8250_port *p)
> +{
> +       unsigned char mcr = serial_in(p, UART_MCR);
> +
> +       if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND)
> +               mcr |= UART_MCR_RTS;
> +       else
> +               mcr &= ~UART_MCR_RTS;
> +       serial_out(p, UART_MCR, mcr);
> +}
> +
> +static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
> +{
> +       unsigned char mcr = serial_in(p, UART_MCR);
> +
> +       if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
> +               mcr |= UART_MCR_RTS;
> +       else
> +               mcr &= ~UART_MCR_RTS;
> +       serial_out(p, UART_MCR, mcr);
> +}
> +
> +static void serial8250_em485_handle_start_tx(unsigned long arg);
> +static void serial8250_em485_handle_stop_tx(unsigned long arg);
> +
>  void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
>  {
>         serial8250_clear_fifos(p);
> @@ -528,6 +554,42 @@ void serial8250_rpm_put(struct uart_8250_port *p)
>  }
>  EXPORT_SYMBOL_GPL(serial8250_rpm_put);
>
> +int serial8250_em485_init(struct uart_8250_port *p)
> +{
> +       if (p->rs485_emul != NULL)
> +               return 0;
> +
> +       p->rs485_emul = kmalloc(sizeof(struct uart_8250_rs485_emul), GFP_KERNEL);
> +       if (p->rs485_emul == NULL)
> +               return -ENOMEM;
> +
> +       init_timer(&p->rs485_emul->stop_tx_timer);
> +       p->rs485_emul->stop_tx_timer.function = serial8250_em485_handle_stop_tx;
> +       p->rs485_emul->stop_tx_timer.data = (unsigned long)p;
> +       p->rs485_emul->stop_tx_timer.flags |= TIMER_IRQSAFE;
> +       init_timer(&p->rs485_emul->start_tx_timer);
> +       p->rs485_emul->start_tx_timer.function = serial8250_em485_handle_start_tx;
> +       p->rs485_emul->start_tx_timer.data = (unsigned long)p;
> +       p->rs485_emul->start_tx_timer.flags |= TIMER_IRQSAFE;
> +
> +       serial8250_em485_rts_after_send(p);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(serial8250_em485_init);
> +void serial8250_em485_destroy(struct uart_8250_port *p)
> +{
> +       if (p->rs485_emul == NULL)
> +               return;
> +
> +       del_timer_sync(&p->rs485_emul->start_tx_timer);
> +       del_timer_sync(&p->rs485_emul->stop_tx_timer);
> +
> +       kfree(p->rs485_emul);
> +       p->rs485_emul = NULL;
> +}
> +EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
> +
>  /*
>   * These two wrappers ensure that enable_runtime_pm_tx() can be called more than
>   * once and disable_runtime_pm_tx() will still disable RPM because the fifo is
> @@ -1293,7 +1355,61 @@ static void serial8250_stop_rx(struct uart_port *port)
>         serial8250_rpm_put(up);
>  }
>
> -static inline void __stop_tx(struct uart_8250_port *p)
> +static __u32 __start_tx_rs485(struct uart_8250_port *p)
> +{
> +       if (!serial8250_em485_enabled(p))
> +               return 0;
> +
> +       if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
> +               serial8250_stop_rx(&p->port);
> +
> +       del_timer_sync(&p->rs485_emul->stop_tx_timer);
> +
> +       if (!!(p->port.rs485.flags & SER_RS485_RTS_ON_SEND) != !!(serial_in(p, UART_MCR) & UART_MCR_RTS)) {
> +               serial8250_em485_rts_on_send(p);
> +               return p->port.rs485.delay_rts_before_send;
> +       }
> +
> +       return 0;
> +}
> +
> +static inline void __do_stop_tx_rs485(struct uart_8250_port *p)
> +{
> +       if (!serial8250_em485_enabled(p))
> +               return;
> +
> +       serial8250_em485_rts_after_send(p);
> +       /*
> +       * Empty the RX FIFO, we are not interested in anything
> +       * received during the half-duplex transmission.
> +       */
> +       if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
> +               serial8250_clear_fifos(p);
> +}
> +
> +static void serial8250_em485_handle_stop_tx(unsigned long arg)
> +{
> +       struct uart_8250_port *p = (struct uart_8250_port *)arg;
> +
> +       __do_stop_tx_rs485(p);
> +}
> +
> +static inline void __stop_tx_rs485(struct uart_8250_port *p)
> +{
> +       if (!serial8250_em485_enabled(p))
> +               return;
> +
> +       del_timer_sync(&p->rs485_emul->start_tx_timer);
> +
> +       /* __do_stop_tx_rs485 is going to set RTS according to config AND flush RX FIFO if required */
> +       if (p->port.rs485.delay_rts_after_send > 0) {
> +               mod_timer(&p->rs485_emul->stop_tx_timer, jiffies + p->port.rs485.delay_rts_after_send * HZ / 1000);
> +       } else {
> +               __do_stop_tx_rs485(p);
> +       }
> +}
> +
> +static inline void __do_stop_tx(struct uart_8250_port *p)
>  {
>         if (p->ier & UART_IER_THRI) {
>                 p->ier &= ~UART_IER_THRI;
> @@ -1302,6 +1418,21 @@ static inline void __stop_tx(struct uart_8250_port *p)
>         }
>  }
>
> +static inline void __stop_tx(struct uart_8250_port *p)
> +{
> +       if (serial8250_em485_enabled(p)) {
> +               unsigned char lsr = serial_in(p, UART_LSR);
> +       /* To provide required timeing and allow FIFO transfer,
> +        * __stop_tx_rs485 must be called only when both FIFO and shift register
> +        * are empty. It is for device driver to enable interrupt on TEMT.
> +        */
> +               if (!((lsr & UART_LSR_TEMT) && (lsr & UART_LSR_THRE)))
> +                       return;
> +       }
> +       __do_stop_tx(p);
> +       __stop_tx_rs485(p);
> +}
> +
>  static void serial8250_stop_tx(struct uart_port *port)
>  {
>         struct uart_8250_port *up = up_to_u8250p(port);
> @@ -1319,12 +1450,10 @@ static void serial8250_stop_tx(struct uart_port *port)
>         serial8250_rpm_put(up);
>  }
>
> -static void serial8250_start_tx(struct uart_port *port)
> +static inline void __start_tx(struct uart_port *port)
>  {
>         struct uart_8250_port *up = up_to_u8250p(port);
>
> -       serial8250_rpm_get_tx(up);
> -
>         if (up->dma && !up->dma->tx_dma(up))
>                 return;
>
> @@ -1350,6 +1479,30 @@ static void serial8250_start_tx(struct uart_port *port)
>         }
>  }
>
> +static void serial8250_em485_handle_start_tx(unsigned long arg)
> +{
> +       struct uart_8250_port *p = (struct uart_8250_port *)arg;
> +
> +       __start_tx(&p->port);
> +}
> +
> +static void serial8250_start_tx(struct uart_port *port)
> +{
> +       struct uart_8250_port *up = up_to_u8250p(port);
> +       __u32 delay;
> +
> +       serial8250_rpm_get_tx(up);
> +
> +       if (up->rs485_emul && timer_pending(&up->rs485_emul->start_tx_timer))
> +               return;
> +
> +       if (up->rs485_emul && (delay = __start_tx_rs485(up))) {
> +               mod_timer(&up->rs485_emul->start_tx_timer, jiffies + delay * HZ / 1000);
> +       } else {
> +               __start_tx(port);
> +       }
> +}
> +
>  static void serial8250_throttle(struct uart_port *port)
>  {
>         port->throttle(port);
> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index faa0e03..99e59fc 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -76,6 +76,11 @@ struct uart_8250_ops {
>         void            (*release_irq)(struct uart_8250_port *);
>  };
>
> +struct uart_8250_rs485_emul {
> +       struct timer_list       start_tx_timer; /* "rs485 start tx" timer */
> +       struct timer_list       stop_tx_timer; /* "rs485 stop tx" timer */
> +};
> +
>  /*
>   * This should be used by drivers which want to register
>   * their own 8250 ports without registering their own
> @@ -122,6 +127,8 @@ struct uart_8250_port {
>         /* 8250 specific callbacks */
>         int                     (*dl_read)(struct uart_8250_port *);
>         void                    (*dl_write)(struct uart_8250_port *, int);
> +
> +       struct uart_8250_rs485_emul *rs485_emul;
>  };
>
>  static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
> --
> 2.6.3
>



-- 
With Best Regards,
Andy Shevchenko
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