serial: liteuart: add IRQ support for the RX path

Add support for IRQ-driven RX. Support for the TX path will be added
in a separate commit.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221123130500.1030189-13-gsomlo@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
index 0b9d96e..8685c97 100644 (file)
--- a/drivers/tty/serial/liteuart.c
+++ b/drivers/tty/serial/liteuart.c
@@ -7,6 +7,7 @@
 
 #include <linux/bits.h>
 #include <linux/console.h>
+#include <linux/interrupt.h>
 #include <linux/litex.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -46,6 +47,7 @@ struct liteuart_port {
        struct uart_port port;
        struct timer_list timer;
        u32 id;
+       u8 irq_reg;
 };
 
 #define to_liteuart_port(port) container_of(port, struct liteuart_port, port)
@@ -76,6 +78,19 @@ static void liteuart_putchar(struct uart_port *port, unsigned char ch)
        litex_write8(port->membase + OFF_RXTX, ch);
 }
 
+static void liteuart_update_irq_reg(struct uart_port *port, bool set, u8 mask)
+{
+       struct liteuart_port *uart = to_liteuart_port(port);
+
+       if (set)
+               uart->irq_reg |= mask;
+       else
+               uart->irq_reg &= ~mask;
+
+       if (port->irq)
+               litex_write8(port->membase + OFF_EV_ENABLE, uart->irq_reg);
+}
+
 static void liteuart_stop_tx(struct uart_port *port)
 {
 }
@@ -129,13 +144,32 @@ static void liteuart_rx_chars(struct uart_port *port)
        tty_flip_buffer_push(&port->state->port);
 }
 
+static irqreturn_t liteuart_interrupt(int irq, void *data)
+{
+       struct liteuart_port *uart = data;
+       struct uart_port *port = &uart->port;
+       unsigned long flags;
+       u8 isr;
+
+       /*
+        * if polling, the context would be "in_serving_softirq", so use
+        * irq[save|restore] spin_lock variants to cover all possibilities
+        */
+       spin_lock_irqsave(&port->lock, flags);
+       isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
+       if (isr & EV_RX)
+               liteuart_rx_chars(port);
+       spin_unlock_irqrestore(&port->lock, flags);
+
+       return IRQ_RETVAL(isr);
+}
+
 static void liteuart_timer(struct timer_list *t)
 {
        struct liteuart_port *uart = from_timer(uart, t, timer);
        struct uart_port *port = &uart->port;
 
-       liteuart_rx_chars(port);
-
+       liteuart_interrupt(0, port);
        mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
 }
 
@@ -161,19 +195,46 @@ static unsigned int liteuart_get_mctrl(struct uart_port *port)
 static int liteuart_startup(struct uart_port *port)
 {
        struct liteuart_port *uart = to_liteuart_port(port);
+       unsigned long flags;
+       int ret;
+
+       if (port->irq) {
+               ret = request_irq(port->irq, liteuart_interrupt, 0,
+                                 KBUILD_MODNAME, uart);
+               if (ret) {
+                       dev_warn(port->dev,
+                               "line %d irq %d failed: switch to polling\n",
+                               port->line, port->irq);
+                       port->irq = 0;
+               }
+       }
 
-       /* disable events */
-       litex_write8(port->membase + OFF_EV_ENABLE, 0);
+       spin_lock_irqsave(&port->lock, flags);
+       /* only enabling rx irqs during startup */
+       liteuart_update_irq_reg(port, true, EV_RX);
+       spin_unlock_irqrestore(&port->lock, flags);
 
-       /* prepare timer for polling */
-       timer_setup(&uart->timer, liteuart_timer, 0);
-       mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
+       if (!port->irq) {
+               timer_setup(&uart->timer, liteuart_timer, 0);
+               mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
+       }
 
        return 0;
 }
 
 static void liteuart_shutdown(struct uart_port *port)
 {
+       struct liteuart_port *uart = to_liteuart_port(port);
+       unsigned long flags;
+
+       spin_lock_irqsave(&port->lock, flags);
+       liteuart_update_irq_reg(port, false, EV_RX | EV_TX);
+       spin_unlock_irqrestore(&port->lock, flags);
+
+       if (port->irq)
+               free_irq(port->irq, port);
+       else
+               del_timer_sync(&uart->timer);
 }
 
 static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
@@ -262,6 +323,12 @@ static int liteuart_probe(struct platform_device *pdev)
                goto err_erase_id;
        }
 
+       ret = platform_get_irq_optional(pdev, 0);
+       if (ret < 0 && ret != -ENXIO)
+               return ret;
+       if (ret > 0)
+               port->irq = ret;
+
        /* values not from device tree */
        port->dev = &pdev->dev;
        port->iotype = UPIO_MEM;