gpio: of: support gpio-ranges for multiple gpiochip devices

Some drivers (e.g. gpio-mt7621 and gpio-brcmstb) have multiple
gpiochip banks within a single device. Unfortunately, the
gpio-ranges property of the device node was being applied to
every gpiochip of the device with device relative GPIO offset
values rather than gpiochip relative GPIO offset values.

This commit makes use of the gpio_chip offset value which can be
non-zero for such devices to split the device node gpio-ranges
property into GPIO offset ranges that can be applied to each
of the relevant gpiochips of the device.

Signed-off-by: Doug Berger <[e-mail]>
Acked-by: Florian Fainelli <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpiolib-of.c

···
 	struct of_phandle_args pinspec;
 	struct pinctrl_dev *pctldev;
 	struct device_node *np;
-	int index = 0, ret;
+	int index = 0, ret, trim;
 	const char *name;
 	static const char group_names_propname[] = "gpio-ranges-group-names";
 	struct property *group_names;
···
 		if (!pctldev)
 			return -EPROBE_DEFER;
 
+		/* Ignore ranges outside of this GPIO chip */
+		if (pinspec.args[0] >= (chip->offset + chip->ngpio))
+			continue;
+		if (pinspec.args[0] + pinspec.args[2] <= chip->offset)
+			continue;
+
 		if (pinspec.args[2]) {
+			/* npins != 0: linear range */
 			if (group_names) {
 				of_property_read_string_index(np,
 						group_names_propname,
···
 					break;
 				}
 			}
-			/* npins != 0: linear range */
+
+			/* Trim the range to fit this GPIO chip */
+			if (chip->offset > pinspec.args[0]) {
+				trim = chip->offset - pinspec.args[0];
+				pinspec.args[2] -= trim;
+				pinspec.args[1] += trim;
+				pinspec.args[0] = 0;
+			} else {
+				pinspec.args[0] -= chip->offset;
+			}
+			if ((pinspec.args[0] + pinspec.args[2]) > chip->ngpio)
+				pinspec.args[2] = chip->ngpio - pinspec.args[0];
+
 			ret = gpiochip_add_pin_range(chip,
 					pinctrl_dev_get_devname(pctldev),
 					pinspec.args[0],