[PATCH v2] serial: max310x: implement gpio_chip::get_direction()

[Tapio Reijonen]

It's strongly recommended for GPIO drivers to always implement the
.get_direction() callback - even when the direction is tracked in
software. The GPIO core emits a warning when the callback is missing
and a user reads the direction of a line, e.g. via
/sys/kernel/debug/gpio.

The MAX310X keeps the GPIO direction in the GPIOCFG register (a set bit
selects output), which the existing direction_input/output callbacks
already program, so the current direction can be read back directly.

Fixes: f65444187a66 ("serial: New serial driver MAX310X")
Signed-off-by: Tapio Reijonen <tapio.reijonen@xxxxxxxxxxx>
---
Found and HW-tested on an i.MX6 SoloX board with a MAX14830 over SPI:
without this, "cat /sys/kernel/debug/gpio" triggers the gpiolib.c:429
WARNING (tainting the kernel W) on each queried MAX14830 line; with it
applied the lines report their in/out direction and the WARNING is gone.
---
Changes in v2:
- Address Hugo Villeneuve's review: use BIT(offset % 4) and put the
  return statement on a single line.
- Rebase onto v7.1-rc7.
- Link to v1: https://lore.kernel.org/r/20260602-b4-serial-max310x-gpio-get-direction-v1-1-23bf84e8ee14@xxxxxxxxxxx
---
 drivers/tty/serial/max310x.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index ac7d3f197c3a5ce3531d5607f48e21a807314021..09b9ab57d2b4479da90fba178b093008f4b57bb9 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -1212,6 +1212,17 @@ static int max310x_gpio_set(struct gpio_chip *chip, unsigned int offset,
 	return 0;
 }
 
+static int max310x_gpio_get_direction(struct gpio_chip *chip, unsigned int offset)
+{
+	struct max310x_port *s = gpiochip_get_data(chip);
+	struct uart_port *port = &s->p[offset / 4].port;
+	unsigned int val;
+
+	val = max310x_port_read(port, MAX310X_GPIOCFG_REG);
+
+	return val & BIT(offset % 4) ? GPIO_LINE_DIRECTION_OUT : GPIO_LINE_DIRECTION_IN;
+}
+
 static int max310x_gpio_direction_input(struct gpio_chip *chip, unsigned int offset)
 {
 	struct max310x_port *s = gpiochip_get_data(chip);
@@ -1421,6 +1432,7 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 	s->gpio.owner		= THIS_MODULE;
 	s->gpio.parent		= dev;
 	s->gpio.label		= devtype->name;
+	s->gpio.get_direction	= max310x_gpio_get_direction;
 	s->gpio.direction_input	= max310x_gpio_direction_input;
 	s->gpio.get		= max310x_gpio_get;
 	s->gpio.direction_output= max310x_gpio_direction_output;

---
base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
change-id: 20260602-b4-serial-max310x-gpio-get-direction-b10ee5be4f24

Best regards,
-- 
Tapio Reijonen <tapio.reijonen@xxxxxxxxxxx>