pinctrl: mcp23s08: Add optional reset GPIO

The MCP23x port expander RESET# line can be connected to a host GPIO.
The optional reset-gpio must be set to LOW if the reset is asserted
at probing time.

On page 5 in the datasheet [0] the "Device Active After Reset high"
time is specified at 0 µs. Therefore no waiting is needed after the
reset transition.

[0] https://ww1.microchip.com/downloads/en/DeviceDoc/20001952C.pdf

Signed-off-by: Andreas Kaessens <[email protected]>
Signed-off-by: Darian Biastoch <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Linus Walleij <[email protected]>

Author: akaessens

drivers/pinctrl/pinctrl-mcp23s08.c

@@ -9,6 +9,7 @@
 #include <linux/module.h>
 #include <linux/export.h>
 #include <linux/gpio/driver.h>
+#include <linux/gpio/consumer.h>
 #include <linux/slab.h>
 #include <asm/byteorder.h>
 #include <linux/interrupt.h>
@@ -558,6 +559,8 @@ int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 	mcp->chip.parent = dev;
 	mcp->chip.owner = THIS_MODULE;
 
+	mcp->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
+
 	/* verify MCP_IOCON.SEQOP = 0, so sequential reads work,
 	 * and MCP_IOCON.HAEN = 1, so we work with all chips.
 	 */

drivers/pinctrl/pinctrl-mcp23s08.h

@@ -43,6 +43,7 @@ struct mcp23s08 {
 
 	struct pinctrl_dev	*pctldev;
 	struct pinctrl_desc	pinctrl_desc;
+	struct gpio_desc        *reset_gpio;
 };
 
 extern const struct regmap_config mcp23x08_regmap;