dt-bindings: gpio: alignment with kernel v5.3

Update the binding file for gpio, it is just an alignment
with kernel v5.3.
The U-Boot code example for gpio-hog (not directly linked
to binding) is moved in a new file doc/README.gpio.
[commit 21676b706e99 ("gpio: fixes for gpio-hog support")
& 'commit 4762a9988ede ("gpio: add gpio-hog support")']

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/doc/README.gpio b/doc/README.gpio
new file mode 100644
index 0000000000..548ff37b8c
--- /dev/null
+++ b/doc/README.gpio
@@ -0,0 +1,42 @@
+
+GPIO hog (CONFIG_GPIO_HOG)
+--------
+
+All the GPIO hog are initialized in gpio_hog_probe_all() function called in
+board_r.c just before board_late_init() but you can also acces directly to
+the gpio with gpio_hog_lookup_name().
+
+
+Example, for the device tree:
+
+        tca6416@20 {
+                compatible = "ti,tca6416";
+                reg = <0x20>;
+                #gpio-cells = <2>;
+                gpio-controller;
+
+                env_reset {
+                        gpio-hog;
+                        input;
+                        gpios = <6 GPIO_ACTIVE_LOW>;
+                };
+                boot_rescue {
+                        gpio-hog;
+                        input;
+                        line-name = "foo-bar-gpio";
+                        gpios = <7 GPIO_ACTIVE_LOW>;
+                };
+        };
+
+You can than access the gpio in your board code with:
+
+	struct gpio_desc *desc;
+	int ret;
+
+	ret = gpio_hog_lookup_name("boot_rescue", &desc);
+	if (ret)
+		return;
+	if (dm_gpio_get_value(desc) == 1)
+		printf("\nBooting into Rescue System\n");
+	else if (dm_gpio_get_value(desc) == 0)
+		printf("\nBoot normal\n");