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

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Message-ID: <20241219084638.960253-1-andre.werner@systec-electronic.com>
Date: Thu, 19 Dec 2024 09:46:38 +0100
From: Andre Werner <andre.werner@...tec-electronic.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	hvilleneuve@...onoff.com,
	andy@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	lech.perczak@...lingroup.com,
	Andre Werner <andre.werner@...tec-electronic.com>
Subject: [PATCH] serial: sc16is7xx: Add polling feature if no IRQ usage possible

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@...tec-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