serial: sc16is7xx: Add polling mode if no IRQ pin is available

Fall back to polling mode if no interrupt is configured because there
is no possibility to connect the interrupt pin.
If "interrupts" property is missing in devicetree the driver
uses a delayed worker to pull the state of interrupt status registers.

Signed-off-by: Andre Werner <andre.werner@systec-electronic.com>
Link: https://lore.kernel.org/r/20250110073104.1029633-2-andre.werner@systec-electronic.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index a3093e09309ffe6999eeee8be97e5adbe74c18b5..7b51cdc274fd8cc311d6de4ca37d03d20a4f1fab 100644 (file)
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -314,6 +314,7 @@
 #define SC16IS7XX_FIFO_SIZE            (64)
 #define SC16IS7XX_GPIOS_PER_BANK       4
 
+#define SC16IS7XX_POLL_PERIOD_MS       10
 #define SC16IS7XX_RECONF_MD            BIT(0)
 #define SC16IS7XX_RECONF_IER           BIT(1)
 #define SC16IS7XX_RECONF_RS485         BIT(2)
@@ -348,6 +349,8 @@ struct sc16is7xx_port {
        u8                              mctrl_mask;
        struct kthread_worker           kworker;
        struct task_struct              *kworker_task;
+       struct kthread_delayed_work     poll_work;
+       bool                            polling;
        struct sc16is7xx_one            p[];
 };
 
@@ -861,6 +864,18 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
        return IRQ_HANDLED;
 }
 
+static void sc16is7xx_poll_proc(struct kthread_work *ws)
+{
+       struct sc16is7xx_port *s = container_of(ws, struct sc16is7xx_port, poll_work.work);
+
+       /* Reuse standard IRQ handler. Interrupt ID is unused in this context. */
+       sc16is7xx_irq(0, s);
+
+       /* Setup delay based on SC16IS7XX_POLL_PERIOD_MS */
+       kthread_queue_delayed_work(&s->kworker, &s->poll_work,
+                                  msecs_to_jiffies(SC16IS7XX_POLL_PERIOD_MS));
+}
+
 static void sc16is7xx_tx_proc(struct kthread_work *ws)
 {
        struct uart_port *port = &(to_sc16is7xx_one(ws, tx_work)->port);
@@ -1149,6 +1164,7 @@ static int sc16is7xx_config_rs485(struct uart_port *port, struct ktermios *termi
 static int sc16is7xx_startup(struct uart_port *port)
 {
        struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+       struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
        unsigned int val;
        unsigned long flags;
 
@@ -1211,6 +1227,10 @@ static int sc16is7xx_startup(struct uart_port *port)
        sc16is7xx_enable_ms(port);
        uart_port_unlock_irqrestore(port, flags);
 
+       if (s->polling)
+               kthread_queue_delayed_work(&s->kworker, &s->poll_work,
+                                          msecs_to_jiffies(SC16IS7XX_POLL_PERIOD_MS));
+
        return 0;
 }
 
@@ -1232,6 +1252,9 @@ static void sc16is7xx_shutdown(struct uart_port *port)
 
        sc16is7xx_power(port, 0);
 
+       if (s->polling)
+               kthread_cancel_delayed_work_sync(&s->poll_work);
+
        kthread_flush_worker(&s->kworker);
 }
 
@@ -1538,6 +1561,11 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
        /* Always ask for fixed clock rate from a property. */
        device_property_read_u32(dev, "clock-frequency", &uartclk);
 
+       s->polling = !!irq;
+       if (s->polling)
+               dev_dbg(dev,
+                       "No interrupt pin definition, falling back to polling mode\n");
+
        s->clk = devm_clk_get_optional(dev, NULL);
        if (IS_ERR(s->clk))
                return PTR_ERR(s->clk);
@@ -1665,6 +1693,12 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
                goto out_ports;
 #endif
 
+       if (s->polling) {
+               /* Initialize kernel thread for polling */
+               kthread_init_delayed_work(&s->poll_work, sc16is7xx_poll_proc);
+               return 0;
+       }
+
        /*
         * Setup interrupt. We first try to acquire the IRQ line as level IRQ.
         * If that succeeds, we can allow sharing the interrupt as well.
@@ -1724,6 +1758,9 @@ void sc16is7xx_remove(struct device *dev)
                sc16is7xx_power(&s->p[i].port, 0);
        }
 
+       if (s->polling)
+               kthread_cancel_delayed_work_sync(&s->poll_work);
+
        kthread_flush_worker(&s->kworker);
        kthread_stop(s->kworker_task);