gpio: sim: allow to mark simulated lines as invalid

Add a new line-level, boolean property to the gpio-sim configfs
interface called 'valid'. It's set by default and the user can unset it
to make the line be included in the standard `gpio-reserved-ranges`
property when the chip is registered with GPIO core. This allows users
to specify which lines should not be available for requesting as GPIOs.

Link: https://lore.kernel.org/r/20250630130358.40352-1-brgl@bgdev.pl
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/admin-guide/gpio/gpio-sim.rst

@@ -50,8 +50,11 @@ the number of lines exposed by this bank.
 
 **Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/name``
 
-This group represents a single line at the offset Y. The 'name' attribute
-allows to set the line name as represented by the 'gpio-line-names' property.
+**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/valid``
+
+This group represents a single line at the offset Y. The ``valid`` attribute
+indicates whether the line can be used as GPIO. The ``name`` attribute allows
+to set the line name as represented by the 'gpio-line-names' property.
 
 **Item:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog``
 

drivers/gpio/gpio-sim.c

@@ -39,7 +39,7 @@
 #include "dev-sync-probe.h"
 
 #define GPIO_SIM_NGPIO_MAX	1024
-#define GPIO_SIM_PROP_MAX	4 /* Max 3 properties + sentinel. */
+#define GPIO_SIM_PROP_MAX	5 /* Max 4 properties + sentinel. */
 #define GPIO_SIM_NUM_ATTRS	3 /* value, pull and sentinel */
 
 static DEFINE_IDA(gpio_sim_ida);
@@ -629,6 +629,7 @@ struct gpio_sim_line {
 
 	unsigned int offset;
 	char *name;
+	bool valid;
 
 	/* There can only be one hog per line. */
 	struct gpio_sim_hog *hog;
@@ -744,6 +745,36 @@ gpio_sim_set_line_names(struct gpio_sim_bank *bank, char **line_names)
 	}
 }
 
+static unsigned int gpio_sim_get_reserved_ranges_size(struct gpio_sim_bank *bank)
+{
+	struct gpio_sim_line *line;
+	unsigned int size = 0;
+
+	list_for_each_entry(line, &bank->line_list, siblings) {
+		if (line->valid)
+			continue;
+
+		size += 2;
+	}
+
+	return size;
+}
+
+static void gpio_sim_set_reserved_ranges(struct gpio_sim_bank *bank,
+					 u32 *ranges)
+{
+	struct gpio_sim_line *line;
+	int i = 0;
+
+	list_for_each_entry(line, &bank->line_list, siblings) {
+		if (line->valid)
+			continue;
+
+		ranges[i++] = line->offset;
+		ranges[i++] = 1;
+	}
+}
+
 static void gpio_sim_remove_hogs(struct gpio_sim_device *dev)
 {
 	struct gpiod_hog *hog;
@@ -844,9 +875,10 @@ static struct fwnode_handle *
 gpio_sim_make_bank_swnode(struct gpio_sim_bank *bank,
 			  struct fwnode_handle *parent)
 {
+	unsigned int prop_idx = 0, line_names_size, ranges_size;
 	struct property_entry properties[GPIO_SIM_PROP_MAX];
-	unsigned int prop_idx = 0, line_names_size;
 	char **line_names __free(kfree) = NULL;
+	u32 *ranges __free(kfree) = NULL;
 
 	memset(properties, 0, sizeof(properties));
 
@@ -870,6 +902,19 @@ gpio_sim_make_bank_swnode(struct gpio_sim_bank *bank,
 						line_names, line_names_size);
 	}
 
+	ranges_size = gpio_sim_get_reserved_ranges_size(bank);
+	if (ranges_size) {
+		ranges = kcalloc(ranges_size, sizeof(u32), GFP_KERNEL);
+		if (!ranges)
+			return ERR_PTR(-ENOMEM);
+
+		gpio_sim_set_reserved_ranges(bank, ranges);
+
+		properties[prop_idx++] = PROPERTY_ENTRY_U32_ARRAY_LEN(
+						"gpio-reserved-ranges",
+						ranges, ranges_size);
+	}
+
 	return fwnode_create_software_node(properties, parent);
 }
 
@@ -1189,8 +1234,41 @@ static ssize_t gpio_sim_line_config_name_store(struct config_item *item,
 
 CONFIGFS_ATTR(gpio_sim_line_config_, name);
 
+static ssize_t
+gpio_sim_line_config_valid_show(struct config_item *item, char *page)
+{
+	struct gpio_sim_line *line = to_gpio_sim_line(item);
+	struct gpio_sim_device *dev = gpio_sim_line_get_device(line);
+
+	guard(mutex)(&dev->lock);
+
+	return sprintf(page, "%c\n", line->valid ? '1' : '0');
+}
+
+static ssize_t gpio_sim_line_config_valid_store(struct config_item *item,
+						const char *page, size_t count)
+{
+	struct gpio_sim_line *line = to_gpio_sim_line(item);
+	struct gpio_sim_device *dev = gpio_sim_line_get_device(line);
+	bool valid;
+	int ret;
+
+	ret = kstrtobool(page, &valid);
+	if (ret)
+		return ret;
+
+	guard(mutex)(&dev->lock);
+
+	line->valid = valid;
+
+	return count;
+}
+
+CONFIGFS_ATTR(gpio_sim_line_config_, valid);
+
 static struct configfs_attribute *gpio_sim_line_config_attrs[] = {
 	&gpio_sim_line_config_attr_name,
+	&gpio_sim_line_config_attr_valid,
 	NULL
 };
 
@@ -1399,6 +1477,7 @@ gpio_sim_bank_config_make_line_group(struct config_group *group,
 
 	line->parent = bank;
 	line->offset = offset;
+	line->valid = true;
 	list_add_tail(&line->siblings, &bank->line_list);
 
 	return &line->group;