gpio: pcf857x: add support for reset-gpios on (most) PCA967x

The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin
that is used to reset the I2C GPIO expander.

One needs to hold this pin low for at least 4us and the reset should be
finished after about 100us according to the datasheet[1]. Once the reset
is done, the "registers and I2C-bus state machine will be held in their
default state until the RESET input is once again HIGH.".

Because the logic is reset, the latch values eventually provided in the
Device Tree via lines-initial-states property are inapplicable so they
are simply ignored if a reset GPIO is provided.

[1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 and fig 22.

Tested-by: Heiko Stuebner <[e-mail]> # RK3588 Tiger Haikou Video Demo
Reviewed-by: Heiko Stuebner <[e-mail]>
Signed-off-by: Quentin Schulz <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-pcf857x.c

···
  * Copyright (C) 2007 David Brownell
  */
 
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/gpio/driver.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
···
 
 static int pcf857x_probe(struct i2c_client *client)
 {
+	struct gpio_desc *reset_gpio;
 	struct pcf857x *gpio;
 	unsigned int n_latch = 0;
 	int status;
-
-	device_property_read_u32(&client->dev, "lines-initial-states", &n_latch);
 
 	/* Allocate, initialize, and register this gpio_chip. */
 	gpio = devm_kzalloc(&client->dev, sizeof(*gpio), GFP_KERNEL);
···
 	gpio->chip.direction_input	= pcf857x_input;
 	gpio->chip.direction_output	= pcf857x_output;
 	gpio->chip.ngpio		= (uintptr_t)i2c_get_match_data(client);
+
+	reset_gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio))
+		return dev_err_probe(&client->dev, PTR_ERR(reset_gpio),
+				     "failed to get reset GPIO\n");
+
+	if (reset_gpio) {
+		/* Reset already held with devm_gpiod_get_optional with GPIOD_OUT_HIGH */
+		fsleep(4); /* tw(rst) > 4us */
+		gpiod_set_value_cansleep(reset_gpio, 0);
+		fsleep(100); /* trst > 100uS */
+
+		/*
+		 * Performing a reset means "The PCA9670 registers and I2C-bus
+		 * state machine will be held in their default state until the
+		 * RESET input is once again HIGH".
+		 *
+		 * This is the same as writing 1 for all pins, which is the same
+		 * as n_latch=0, the default value of the variable.
+		 */
+	} else {
+		device_property_read_u32(&client->dev, "lines-initial-states",
+					 &n_latch);
+	}
 
 	/* NOTE:  the OnSemi jlc1562b is also largely compatible with
 	 * these parts, notably for output.  It has a low-resolution