gpiolib: allow multiple lookup tables per consumer

The GPIO machine lookup mechanism dates back to old ARM board files
where lookup tables would all be defined in a single place. Since then,
lookup tables have also been used to address various DT and ACPI quirks
like missing GPIOs and - as of recently - setting up shared GPIO proxy
devices.

The lookup itself stops when we find the first matching table for a
consumer and - if it doesn't contain the right entry - the lookup fails.

Since the tables can now be defined in multiple places and we can't know
how many there are, effectively limiting a consumer to only a single
lookup table is no longer viable.

Rework the code to always look through all tables matching the consumer.

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

drivers/gpio/gpiolib.c

···
 }
 EXPORT_SYMBOL_GPL(gpiod_remove_hogs);
 
-static struct gpiod_lookup_table *gpiod_find_lookup_table(struct device *dev)
+static bool gpiod_match_lookup_table(struct device *dev,
+				     const struct gpiod_lookup_table *table)
 {
 	const char *dev_id = dev ? dev_name(dev) : NULL;
-	struct gpiod_lookup_table *table;
 
-	list_for_each_entry(table, &gpio_lookup_list, list) {
-		if (table->dev_id && dev_id) {
-			/*
-			 * Valid strings on both ends, must be identical to have
-			 * a match
-			 */
-			if (!strcmp(table->dev_id, dev_id))
-				return table;
-		} else {
-			/*
-			 * One of the pointers is NULL, so both must be to have
-			 * a match
-			 */
-			if (dev_id == table->dev_id)
-				return table;
-		}
+	lockdep_assert_held(&gpio_lookup_lock);
+
+	if (table->dev_id && dev_id) {
+		/*
+		 * Valid strings on both ends, must be identical to have
+		 * a match
+		 */
+		if (!strcmp(table->dev_id, dev_id))
+			return true;
+	} else {
+		/*
+		 * One of the pointers is NULL, so both must be to have
+		 * a match
+		 */
+		if (dev_id == table->dev_id)
+			return true;
 	}
 
-	return NULL;
+	return false;
 }
 
-static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
-				    unsigned int idx, unsigned long *flags)
+static struct gpio_desc *gpio_desc_table_match(struct device *dev, const char *con_id,
+					       unsigned int idx, unsigned long *flags,
+					       struct gpiod_lookup_table *table)
 {
-	struct gpio_desc *desc = ERR_PTR(-ENOENT);
-	struct gpiod_lookup_table *table;
+	struct gpio_desc *desc;
 	struct gpiod_lookup *p;
 	struct gpio_chip *gc;
 
-	guard(mutex)(&gpio_lookup_lock);
-
-	table = gpiod_find_lookup_table(dev);
-	if (!table)
-		return desc;
+	lockdep_assert_held(&gpio_lookup_lock);
 
 	for (p = &table->table[0]; p->key; p++) {
 		/* idx must always match exactly */
···
 		return desc;
 	}
 
+	return NULL;
+}
+
+static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
+				    unsigned int idx, unsigned long *flags)
+{
+	struct gpio_desc *desc = ERR_PTR(-ENOENT);
+	struct gpiod_lookup_table *table;
+
+	guard(mutex)(&gpio_lookup_lock);
+
+	list_for_each_entry(table, &gpio_lookup_list, list) {
+		if (!gpiod_match_lookup_table(dev, table))
+			continue;
+
+		desc = gpio_desc_table_match(dev, con_id, idx, flags, table);
+		if (!desc)
+			continue;
+
+		/* On IS_ERR() or match. */
+		return desc;
+	}
+
 	return desc;
 }
 
···
 	unsigned int count = 0;
 
 	scoped_guard(mutex, &gpio_lookup_lock) {
-		table = gpiod_find_lookup_table(dev);
-		if (!table)
-			return -ENOENT;
+		list_for_each_entry(table, &gpio_lookup_list, list) {
+			if (!gpiod_match_lookup_table(dev, table))
+				continue;
 
-		for (p = &table->table[0]; p->key; p++) {
-			if ((con_id && p->con_id && !strcmp(con_id, p->con_id)) ||
-			    (!con_id && !p->con_id))
-				count++;
+			for (p = &table->table[0]; p->key; p++) {
+				if ((con_id && p->con_id &&
+				    !strcmp(con_id, p->con_id)) ||
+				    (!con_id && !p->con_id))
+					count++;
+			}
 		}
 	}