[PATCH] serial: sc16is7xx: Add polling feature if no IRQ usage possible

[Andre Werner <andre.werner@systec-electronic.com>]

Fall back to polling mode if no interrupt is configured because not
possible. If "interrupts" property is missing in devicetree the driver
uses a delayed worker to pull state of interrupt status registers.

Signed-off-by: Andre Werner <andre.werner@systec-electronic.com>
---
This driver was tested on Linux 5.10. We had a custom board that was not
able to connect the interrupt port. Only I2C was available.
---
---
 drivers/tty/serial/sc16is7xx.c | 40 ++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index a3093e09309f..31962fdca178 100644
--- 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 10 /*ms*/
 #define SC16IS7XX_RECONF_MD		BIT(0)
 #define SC16IS7XX_RECONF_IER		BIT(1)
 #define SC16IS7XX_RECONF_RS485		BIT(2)
@@ -348,6 +349,9 @@ struct sc16is7xx_port {
 	u8				mctrl_mask;
 	struct kthread_worker		kworker;
 	struct task_struct		*kworker_task;
+	struct kthread_delayed_work	poll_work;
+	bool polling;
+	bool shutdown;
 	struct sc16is7xx_one		p[];
 };
 
@@ -861,6 +865,19 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static void sc16is7xx_transmission_poll(struct kthread_work *work)
+{
+	struct sc16is7xx_port *s = container_of(work, struct sc16is7xx_port, poll_work.work);
+
+	/* Resuse standard IRQ handler. Interrupt ID is unused in this context. */
+	sc16is7xx_irq(0, s);
+
+	/* setup delay based on SC16IS7XX_POLL_PERIOD */
+	if (!s->shutdown)
+		kthread_queue_delayed_work(&s->kworker, &s->poll_work,
+					   msecs_to_jiffies(SC16IS7XX_POLL_PERIOD));
+}
+
 static void sc16is7xx_tx_proc(struct kthread_work *ws)
 {
 	struct uart_port *port = &(to_sc16is7xx_one(ws, tx_work)->port);
@@ -1149,6 +1166,7 @@ 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;
 
@@ -1210,6 +1228,11 @@ static int sc16is7xx_startup(struct uart_port *port)
 	uart_port_lock_irqsave(port, &flags);
 	sc16is7xx_enable_ms(port);
 	uart_port_unlock_irqrestore(port, flags);
+	if (s->polling) {
+		s->shutdown = false;
+		kthread_queue_delayed_work(&s->kworker, &s->poll_work,
+					   msecs_to_jiffies(SC16IS7XX_POLL_PERIOD));
+	}
 
 	return 0;
 }
@@ -1232,6 +1255,10 @@ static void sc16is7xx_shutdown(struct uart_port *port)
 
 	sc16is7xx_power(port, 0);
 
+	if (s->polling) {
+		s->shutdown = true;
+		kthread_cancel_delayed_work_sync(&s->poll_work);
+	}
 	kthread_flush_worker(&s->kworker);
 }
 
@@ -1537,7 +1564,13 @@ 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 = !device_property_present(dev, "interrupts");
 
+	if (s->polling) {
+		dev_warn(dev,
+			 "No interrupt definition found. Falling back to polling mode.\n");
+		irq = 0;
+	}
 	s->clk = devm_clk_get_optional(dev, NULL);
 	if (IS_ERR(s->clk))
 		return PTR_ERR(s->clk);
@@ -1664,6 +1697,11 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
 	if (ret)
 		goto out_ports;
 #endif
+	if (s->polling) {
+		/* Initialize Kernel timer for polling */
+		kthread_init_delayed_work(&s->poll_work, sc16is7xx_transmission_poll);
+		return 0;
+	}
 
 	/*
 	 * Setup interrupt. We first try to acquire the IRQ line as level IRQ.
@@ -1724,6 +1762,8 @@ 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);
 
-- 
2.47.1