serial: amba-pl011: add RS485 support

Add basic support for RS485: Provide a callback to configure RS485
settings. Handle the RS485 specific part in the functions
pl011_rs485_tx_start() and pl011_rs485_tx_stop() which extend the generic
start/stop callbacks.
Beside via IOCTL from userspace RS485 can be enabled by means of the
device tree property "rs485-enabled-at-boot-time".

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Link: https://lore.kernel.org/r/20210630225644.3744-1-LinoSanfilippo@gmx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index e14f3378b8a0e65bd33a2cf635c72aec1ed33766..d361cd84ff8cfecf95b4d0b6b433796bdf700c24 100644 (file)
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -265,6 +265,8 @@ struct uart_amba_port {
        unsigned int            old_cr;         /* state during shutdown */
        unsigned int            fixed_baud;     /* vendor-set fixed baud rate */
        char                    type[12];
+       bool                    rs485_tx_started;
+       unsigned int            rs485_tx_drain_interval; /* usecs */
 #ifdef CONFIG_DMA_ENGINE
        /* DMA stuff */
        bool                    using_tx_dma;
@@ -275,6 +277,8 @@ struct uart_amba_port {
 #endif
 };
 
+static unsigned int pl011_tx_empty(struct uart_port *port);
+
 static unsigned int pl011_reg_to_offset(const struct uart_amba_port *uap,
        unsigned int reg)
 {
@@ -1282,6 +1286,42 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap)
 #define pl011_dma_flush_buffer NULL
 #endif
 
+static void pl011_rs485_tx_stop(struct uart_amba_port *uap)
+{
+       struct uart_port *port = &uap->port;
+       int i = 0;
+       u32 cr;
+
+       /* Wait until hardware tx queue is empty */
+       while (!pl011_tx_empty(port)) {
+               if (i == port->fifosize) {
+                       dev_warn(port->dev,
+                                "timeout while draining hardware tx queue\n");
+                       break;
+               }
+
+               udelay(uap->rs485_tx_drain_interval);
+               i++;
+       }
+
+       if (port->rs485.delay_rts_after_send)
+               mdelay(port->rs485.delay_rts_after_send);
+
+       cr = pl011_read(uap, REG_CR);
+
+       if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+               cr &= ~UART011_CR_RTS;
+       else
+               cr |= UART011_CR_RTS;
+
+       /* Disable the transmitter and reenable the transceiver */
+       cr &= ~UART011_CR_TXE;
+       cr |= UART011_CR_RXE;
+       pl011_write(cr, uap, REG_CR);
+
+       uap->rs485_tx_started = false;
+}
+
 static void pl011_stop_tx(struct uart_port *port)
 {
        struct uart_amba_port *uap =
@@ -1290,6 +1330,9 @@ static void pl011_stop_tx(struct uart_port *port)
        uap->im &= ~UART011_TXIM;
        pl011_write(uap->im, uap, REG_IMSC);
        pl011_dma_tx_stop(uap);
+
+       if ((port->rs485.flags & SER_RS485_ENABLED) && uap->rs485_tx_started)
+               pl011_rs485_tx_stop(uap);
 }
 
 static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq);
@@ -1380,6 +1423,32 @@ static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c,
        return true;
 }
 
+static void pl011_rs485_tx_start(struct uart_amba_port *uap)
+{
+       struct uart_port *port = &uap->port;
+       u32 cr;
+
+       /* Enable transmitter */
+       cr = pl011_read(uap, REG_CR);
+       cr |= UART011_CR_TXE;
+
+       /* Disable receiver if half-duplex */
+       if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
+               cr &= ~UART011_CR_RXE;
+
+       if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
+               cr &= ~UART011_CR_RTS;
+       else
+               cr |= UART011_CR_RTS;
+
+       pl011_write(cr, uap, REG_CR);
+
+       if (port->rs485.delay_rts_before_send)
+               mdelay(port->rs485.delay_rts_before_send);
+
+       uap->rs485_tx_started = true;
+}
+
 /* Returns true if tx interrupts have to be (kept) enabled  */
 static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 {
@@ -1397,6 +1466,10 @@ static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
                return false;
        }
 
+       if ((uap->port.rs485.flags & SER_RS485_ENABLED) &&
+           !uap->rs485_tx_started)
+               pl011_rs485_tx_start(uap);
+
        /* If we are using DMA mode, try to send some characters. */
        if (pl011_dma_tx_irq(uap))
                return true;
@@ -1542,6 +1615,9 @@ static void pl011_set_mctrl(struct uart_port *port, unsigned int mctrl)
            container_of(port, struct uart_amba_port, port);
        unsigned int cr;
 
+       if (port->rs485.flags & SER_RS485_ENABLED)
+               mctrl &= ~TIOCM_RTS;
+
        cr = pl011_read(uap, REG_CR);
 
 #define        TIOCMBIT(tiocmbit, uartbit)             \
@@ -1763,7 +1839,17 @@ static int pl011_startup(struct uart_port *port)
 
        /* restore RTS and DTR */
        cr = uap->old_cr & (UART011_CR_RTS | UART011_CR_DTR);
-       cr |= UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE;
+       cr |= UART01x_CR_UARTEN | UART011_CR_RXE;
+
+       if (port->rs485.flags & SER_RS485_ENABLED) {
+               if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+                       cr &= ~UART011_CR_RTS;
+               else
+                       cr |= UART011_CR_RTS;
+       } else {
+               cr |= UART011_CR_TXE;
+       }
+
        pl011_write(cr, uap, REG_CR);
 
        spin_unlock_irq(&uap->port.lock);
@@ -1864,6 +1950,9 @@ static void pl011_shutdown(struct uart_port *port)
 
        pl011_dma_shutdown(uap);
 
+       if ((port->rs485.flags & SER_RS485_ENABLED) && uap->rs485_tx_started)
+               pl011_rs485_tx_stop(uap);
+
        free_irq(uap->port.irq, uap);
 
        pl011_disable_uart(uap);
@@ -1941,6 +2030,7 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
        unsigned int lcr_h, old_cr;
        unsigned long flags;
        unsigned int baud, quot, clkdiv;
+       unsigned int bits;
 
        if (uap->vendor->oversampling)
                clkdiv = 8;
@@ -1991,6 +2081,8 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
        if (uap->fifosize > 1)
                lcr_h |= UART01x_LCRH_FEN;
 
+       bits = tty_get_frame_size(termios->c_cflag);
+
        spin_lock_irqsave(&port->lock, flags);
 
        /*
@@ -1998,11 +2090,21 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
         */
        uart_update_timeout(port, termios->c_cflag, baud);
 
+       /*
+        * Calculate the approximated time it takes to transmit one character
+        * with the given baud rate. We use this as the poll interval when we
+        * wait for the tx queue to empty.
+        */
+       uap->rs485_tx_drain_interval = (bits * 1000 * 1000) / baud;
+
        pl011_setup_status_masks(port, termios);
 
        if (UART_ENABLE_MS(port, termios->c_cflag))
                pl011_enable_ms(port);
 
+       if (port->rs485.flags & SER_RS485_ENABLED)
+               termios->c_cflag &= ~CRTSCTS;
+
        /* first, disable everything */
        old_cr = pl011_read(uap, REG_CR);
        pl011_write(0, uap, REG_CR);
@@ -2124,6 +2226,41 @@ static int pl011_verify_port(struct uart_port *port, struct serial_struct *ser)
        return ret;
 }
 
+static int pl011_rs485_config(struct uart_port *port,
+                             struct serial_rs485 *rs485)
+{
+       struct uart_amba_port *uap =
+               container_of(port, struct uart_amba_port, port);
+
+       /* pick sane settings if the user hasn't */
+       if (!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
+           !(rs485->flags & SER_RS485_RTS_AFTER_SEND)) {
+               rs485->flags |= SER_RS485_RTS_ON_SEND;
+               rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
+       }
+       /* clamp the delays to [0, 100ms] */
+       rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
+       rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
+       memset(rs485->padding, 0, sizeof(rs485->padding));
+
+       if (port->rs485.flags & SER_RS485_ENABLED)
+               pl011_rs485_tx_stop(uap);
+
+       /* Set new configuration */
+       port->rs485 = *rs485;
+
+       /* Make sure auto RTS is disabled */
+       if (port->rs485.flags & SER_RS485_ENABLED) {
+               u32 cr = pl011_read(uap, REG_CR);
+
+               cr &= ~UART011_CR_RTSEN;
+               pl011_write(cr, uap, REG_CR);
+               port->status &= ~UPSTAT_AUTORTS;
+       }
+
+       return 0;
+}
+
 static const struct uart_ops amba_pl011_pops = {
        .tx_empty       = pl011_tx_empty,
        .set_mctrl      = pl011_set_mctrl,
@@ -2588,10 +2725,28 @@ static int pl011_find_free_port(void)
        return -EBUSY;
 }
 
+static int pl011_get_rs485_mode(struct uart_amba_port *uap)
+{
+       struct uart_port *port = &uap->port;
+       struct serial_rs485 *rs485 = &port->rs485;
+       int ret;
+
+       ret = uart_get_rs485_mode(port);
+       if (ret)
+               return ret;
+
+       /* clamp the delays to [0, 100ms] */
+       rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
+       rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
+
+       return 0;
+}
+
 static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
                            struct resource *mmiobase, int index)
 {
        void __iomem *base;
+       int ret;
 
        base = devm_ioremap_resource(dev, mmiobase);
        if (IS_ERR(base))
@@ -2608,6 +2763,10 @@ static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
        uap->port.flags = UPF_BOOT_AUTOCONF;
        uap->port.line = index;
 
+       ret = pl011_get_rs485_mode(uap);
+       if (ret)
+               return ret;
+
        amba_ports[index] = uap;
 
        return 0;
@@ -2665,7 +2824,7 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
        uap->port.iotype = vendor->access_32b ? UPIO_MEM32 : UPIO_MEM;
        uap->port.irq = dev->irq[0];
        uap->port.ops = &amba_pl011_pops;
-
+       uap->port.rs485_config = pl011_rs485_config;
        snprintf(uap->type, sizeof(uap->type), "PL011 rev%u", amba_rev(dev));
 
        ret = pl011_setup_port(&dev->dev, uap, &dev->res, portnr);