[PATCH] gpio: serial: max310x: Support open-drain configuration for GPIOs

[Jan Kundrát <jan.kundrat@xxxxxxxxx>]

The push-pull vs. open-drain are the only supported output modes. The
inputs are always unconditionally equipped with weak pull-downs. That's
the only mode, so there's probably no point in exporting that. I wonder
if it's worthwhile to provide a custom dbg_show method to indicate the
current status of the outputs, though.

This patch and [1] for i2c-gpio together make it possible to bit-bang an
I2C bus over GPIOs of an UART which is connected via SPI :). Yes, this
is crazy, but it's fast enough (while on a 26Mhz SPI HW bus with a
dual-core 1.6GHz CPU) to drive an I2C bus at 200kHz, according to my
scope.

[1] https://patchwork.ozlabs.org/patch/852591/

Signed-off-by: Jan Kundrát <jan.kundrat@xxxxxxxxx>
---
My suggestion is for this patch to go in via the tty/serial tree; I plan
to send more patches to this driver (and some of them are alreay in
tty-next). --jkt

---
 drivers/tty/serial/max310x.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index d0e55f8456a5..c44387d0625a 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -1187,6 +1187,27 @@ static int max310x_gpio_direction_output(struct gpio_chip *chip,
 	return 0;
 }
 
+static int max310x_gpio_set_config(struct gpio_chip *chip, unsigned int offset,
+				   unsigned long config)
+{
+	struct max310x_port *s = gpiochip_get_data(chip);
+	struct uart_port *port = &s->p[offset / 4].port;
+
+	switch (pinconf_to_config_param(config)) {
+	case PIN_CONFIG_DRIVE_OPEN_DRAIN:
+		max310x_port_update(port, MAX310X_GPIOCFG_REG,
+				1 << ((offset % 4) + 4),
+				1 << ((offset % 4) + 4));
+		return 0;
+	case PIN_CONFIG_DRIVE_PUSH_PULL:
+		max310x_port_update(port, MAX310X_GPIOCFG_REG,
+				1 << ((offset % 4) + 4), 0);
+		return 0;
+	default:
+		return -ENOTSUPP;
+	}
+}
+
 static void max310x_gpio_irq_mask(struct irq_data *d)
 {
 	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
@@ -1426,6 +1447,7 @@ static int max310x_probe(struct device *dev, struct max310x_devtype *devtype,
 	s->gpio.get		= max310x_gpio_get;
 	s->gpio.direction_output= max310x_gpio_direction_output;
 	s->gpio.set		= max310x_gpio_set;
+	s->gpio.set_config	= max310x_gpio_set_config;
 	s->gpio.base		= -1;
 	s->gpio.ngpio		= devtype->nr * 4;
 	s->gpio.can_sleep	= 1;
-- 
2.14.3


--
To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html