[PATCH 1/3] serial: max310x: register GPIO controller before adding UART ports

[Tapio Reijonen]

The MAX310x exposes four GPIOs per UART port via an in-driver
gpio_chip. devm_gpiochip_add_data() used to run after the per-port
uart_add_one_port() loop, so a device-tree consumer referencing one of
the chip's own GPIOs (for example rs485-term-gpios = <&max310x 0 ...>)
could not resolve it during port registration: the GPIO provider it
waits for is the very driver still trying to register, and the lookup
returns -EPROBE_DEFER on its own provider, deferring probe forever.

Split the per-port setup into two passes around the gpio_chip
registration:

  1. Initialise per-port state - port struct fields, regmap binding,
     IRQ disable, work queues. The gpio_chip callbacks dereference
     s->p[i].regmap via to_max310x_port() and become callable as soon
     as the chip is visible to gpiolib, so every entry must be
     populated first.
  2. devm_gpiochip_add_data() - register the gpio_chip.
  3. Allocate a line, uart_add_one_port(), set_bit(), max310x_power().
     Keeping line allocation, registration and set_bit() together
     preserves the existing "bit set <=> port registered" rollback
     invariant that out_uart relies on.

Signed-off-by: Tapio Reijonen <tapio.reijonen@xxxxxxxxxxx>
---
 drivers/tty/serial/max310x.c | 54 +++++++++++++++++++++++++++-----------------
 1 file changed, 33 insertions(+), 21 deletions(-)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index ac7d3f197c3a5ce3531d5607f48e21a807314021..5cb7d01e404663dc25b88bc7b4f8df61be2135ec 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -1364,17 +1364,12 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 
 	dev_dbg(dev, "Reference clock set to %i Hz\n", uartclk);
 
+	/*
+	 * Set up each port's state before registering the gpiochip,
+	 * since the gpiochip callbacks will read s->p[i].regmap as
+	 * soon as gpiolib exposes the controller.
+	 */
 	for (i = 0; i < devtype->nr; i++) {
-		unsigned int line;
-
-		line = find_first_zero_bit(max310x_lines, MAX310X_UART_NRMAX);
-		if (line == MAX310X_UART_NRMAX) {
-			ret = -ERANGE;
-			goto out_uart;
-		}
-
-		/* Initialize port data */
-		s->p[i].port.line	= line;
 		s->p[i].port.dev	= dev;
 		s->p[i].port.irq	= irq;
 		s->p[i].port.type	= PORT_MAX310X;
@@ -1404,20 +1399,16 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 		INIT_WORK(&s->p[i].md_work, max310x_md_proc);
 		/* Initialize queue for changing RS485 mode */
 		INIT_WORK(&s->p[i].rs_work, max310x_rs_proc);
-
-		/* Register port */
-		ret = uart_add_one_port(&max310x_uart, &s->p[i].port);
-		if (ret)
-			goto out_uart;
-
-		set_bit(line, max310x_lines);
-
-		/* Go to suspend mode */
-		max310x_power(&s->p[i].port, 0);
 	}
 
 #ifdef CONFIG_GPIOLIB
-	/* Setup GPIO controller */
+	/*
+	 * Register the GPIO controller before adding the UART ports so
+	 * that consumers referencing the chip's own GPIOs from device
+	 * tree (for example rs485-term-gpios = <&max310x ...>) can
+	 * resolve them at uart_add_one_port() time instead of receiving
+	 * -EPROBE_DEFER from their own provider.
+	 */
 	s->gpio.owner		= THIS_MODULE;
 	s->gpio.parent		= dev;
 	s->gpio.label		= devtype->name;
@@ -1434,6 +1425,27 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 		goto out_uart;
 #endif
 
+	for (i = 0; i < devtype->nr; i++) {
+		unsigned int line;
+
+		line = find_first_zero_bit(max310x_lines, MAX310X_UART_NRMAX);
+		if (line == MAX310X_UART_NRMAX) {
+			ret = -ERANGE;
+			goto out_uart;
+		}
+		s->p[i].port.line = line;
+
+		/* Register port */
+		ret = uart_add_one_port(&max310x_uart, &s->p[i].port);
+		if (ret)
+			goto out_uart;
+
+		set_bit(line, max310x_lines);
+
+		/* Go to suspend mode */
+		max310x_power(&s->p[i].port, 0);
+	}
+
 	/* Setup interrupt */
 	ret = devm_request_threaded_irq(dev, irq, NULL, max310x_ist,
 					IRQF_ONESHOT | IRQF_SHARED, dev_name(dev), s);

-- 
2.47.3