linux-kernel - [PATCH v7] serial: sc16is7xx: Add polling mode if no IRQ pin is available

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Message-ID: <20250116083447.453615-1-andre.werner@systec-electronic.com>
Date: Thu, 16 Jan 2025 09:34:47 +0100
From: Andre Werner <andre.werner@...tec-electronic.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	hvilleneuve@...onoff.com,
	andy@...nel.org,
	devicetree@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	lech.perczak@...lingroup.com,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
	robh@...nel.org,
	Andre Werner <andre.werner@...tec-electronic.com>
Subject: [PATCH v7] 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 no interrupt pin is available the driver uses a delayed worker to
poll the state of interrupt status registers (IIR).

Signed-off-by: Andre Werner <andre.werner@...tec-electronic.com>
Link: https://lore.kernel.org/r/20250110073104.1029633-2-andre.werner@systec-electronic.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
V2:
- Change warning for polling mode to debug log entry
- Correct typo: Resuse -> Reuse
- Format define with missing tabs for SC16IS7XX_POLL_PERIOD
- Format struct declaration sc16is7xx_one_config with missing tabs for polling and shutdown
- Adapt dtbinding with new polling feature
V3:
- Use suffix with units and drop a comment SC16IS7XX_POLL_PERIOD_MS. Sorry for that miss.
- Make Kernel lowercase.
V4:
- Reword commit messages for better understanding.
- Remove 'shutdown' property for canceling delayed worker.
- Rename worker function: sc16is7xx_transmission_poll -> sc16is7xx_poll_proc
- Unify argument for worker functions: kthread_work *work -> kthread_work *ws
V5:
- Replace of_property check with IRQ number check to set polling
  property. This will add support for usage without device tree
  definitions. Thanks for that advice.
- Add blank line es requested.
V6:
- Use polling mode for IRQ numbers <= 0 which encounter no valid IRQ
  were found/defined.
V7:
- Try to improve and unify comments as requested.
- Fix typo in commit message: pull -> poll
---
 drivers/tty/serial/sc16is7xx.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 7b51cdc274fd..348ddc3103cd 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -868,10 +868,12 @@ 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. */
+	/*
+	 * Reuse standard IRQ handler. Interrupt ID is unused in this
+	 * context and set to zero.
+	 */
 	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));
 }
@@ -1561,7 +1563,7 @@ 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;
+	s->polling = (irq <= 0);
 	if (s->polling)
 		dev_dbg(dev,
 			"No interrupt pin definition, falling back to polling mode\n");
@@ -1694,7 +1696,7 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
 #endif
 
 	if (s->polling) {
-		/* Initialize kernel thread for polling */
+		/* Initialize a kthread work struct that is dedicated to polling */
 		kthread_init_delayed_work(&s->poll_work, sc16is7xx_poll_proc);
 		return 0;
 	}
-- 
2.48.0