Revert "gpio: remove of_get_named_gpio() and <linux/of_gpio.h>"

This reverts commit b6420bd5aa.

There are many OOT drivers still using this API, so bring this back
temporarily while all the users are converted to the new descriptor
based GPIO alternative.

Bug: 509877995
Change-Id: I3bbdef1934593f9e03ab1a8970b525bafde26bed
Signed-off-by: Carlos Llamas <cmllamas@google.com>

MAINTAINERS

@@ -10982,6 +10982,7 @@ F:	drivers/gpio/
 F:	include/dt-bindings/gpio/
 F:	include/linux/gpio.h
 F:	include/linux/gpio/
+F:	include/linux/of_gpio.h
 K:	(devm_)?gpio_(request|free|direction|get|set)
 K:	GPIOD_FLAGS_BIT_NONEXCLUSIVE
 K:	devm_gpiod_unhinge

drivers/gpio/TODO

@@ -58,6 +58,34 @@ Work items:
 
 -------------------------------------------------------------------------------
 
+Get rid of <linux/of_gpio.h>
+
+This header and helpers appeared at one point when there was no proper
+driver infrastructure for doing simpler MMIO GPIO devices and there was
+no core support for parsing device tree GPIOs from the core library with
+the [devm_]gpiod_get() calls we have today that will implicitly go into
+the device tree back-end. It is legacy and should not be used in new code.
+
+Work items:
+
+- Change all consumer drivers that #include <linux/of_gpio.h> to
+  #include <linux/gpio/consumer.h> and stop doing custom parsing of the
+  GPIO lines from the device tree. This can be tricky and often involves
+  changing board files, etc.
+
+- Pull semantics for legacy device tree (OF) GPIO lookups into
+  gpiolib-of.c: in some cases subsystems are doing custom flags and
+  lookups for polarity inversion, open drain and what not. As we now
+  handle this with generic OF bindings, pull all legacy handling into
+  gpiolib so the library API becomes narrow and deep and handle all
+  legacy bindings internally. (See e.g. commits 6953c57ab172,
+  6a537d48461d etc)
+
+- Delete <linux/of_gpio.h> when all the above is complete and everything
+  uses <linux/gpio/consumer.h> or <linux/gpio/driver.h> instead.
+
+-------------------------------------------------------------------------------
+
 Collect drivers
 
 Collect GPIO drivers from arch/* and other places that should be placed

drivers/gpio/gpiolib-of.c

@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_gpio.h>
 #include <linux/pinctrl/pinctrl.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -446,6 +447,32 @@ out:
 	return desc;
 }
 
+/**
+ * of_get_named_gpio() - Get a GPIO number to use with GPIO API
+ * @np:		device node to get GPIO from
+ * @propname:	Name of property containing gpio specifier(s)
+ * @index:	index of the GPIO
+ *
+ * **DEPRECATED** This function is deprecated and must not be used in new code.
+ *
+ * Returns:
+ * GPIO number to use with Linux generic GPIO API, or one of the errno
+ * value on the error condition.
+ */
+int of_get_named_gpio(const struct device_node *np, const char *propname,
+		      int index)
+{
+	struct gpio_desc *desc;
+
+	desc = of_get_named_gpiod_flags(np, propname, index, NULL);
+
+	if (IS_ERR(desc))
+		return PTR_ERR(desc);
+	else
+		return desc_to_gpio(desc);
+}
+EXPORT_SYMBOL_GPL(of_get_named_gpio);
+
 /* Converts gpio_lookup_flags into bitmask of GPIO_* values */
 static unsigned long of_convert_gpio_flags(enum of_gpio_flags flags)
 {

include/linux/of_gpio.h

@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * OF helpers for the GPIO API
+ *
+ * Copyright (c) 2007-2008  MontaVista Software, Inc.
+ *
+ * Author: Anton Vorontsov <avorontsov@ru.mvista.com>
+ */
+
+#ifndef __LINUX_OF_GPIO_H
+#define __LINUX_OF_GPIO_H
+
+#include <linux/compiler.h>
+#include <linux/gpio/driver.h>
+#include <linux/gpio.h>		/* FIXME: Shouldn't be here */
+#include <linux/of.h>
+
+struct device_node;
+
+#ifdef CONFIG_OF_GPIO
+
+extern int of_get_named_gpio(const struct device_node *np,
+			     const char *list_name, int index);
+
+#else /* CONFIG_OF_GPIO */
+
+#include <linux/errno.h>
+
+/* Drivers may not strictly depend on the GPIO support, so let them link. */
+static inline int of_get_named_gpio(const struct device_node *np,
+                                   const char *propname, int index)
+{
+	return -ENOSYS;
+}
+
+#endif /* CONFIG_OF_GPIO */
+
+#endif /* __LINUX_OF_GPIO_H */