gpio: sim: implement the dbg_show() callback

Provide a custom implementation of the dbg_show() callback that prints
all requested lines together with their label, direction, value and
bias. This improves the code coverage of GPIOLIB.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/gpio-sim.c

@@ -20,6 +20,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irq_sim.h>
+#include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/minmax.h>
 #include <linux/mod_devicetable.h>
@@ -28,6 +29,7 @@
 #include <linux/notifier.h>
 #include <linux/platform_device.h>
 #include <linux/property.h>
+#include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/string_helpers.h>
@@ -224,6 +226,25 @@ static void gpio_sim_free(struct gpio_chip *gc, unsigned int offset)
 	}
 }
 
+static void gpio_sim_dbg_show(struct seq_file *seq, struct gpio_chip *gc)
+{
+	struct gpio_sim_chip *chip = gpiochip_get_data(gc);
+	const char *label;
+	int i;
+
+	guard(mutex)(&chip->lock);
+
+	for_each_requested_gpio(gc, i, label)
+		seq_printf(seq, " gpio-%-3d (%s) %s,%s\n",
+			   gc->base + i,
+			   label,
+			   test_bit(i, chip->direction_map) ? "input" :
+				test_bit(i, chip->value_map) ? "output-high" :
+							       "output-low",
+			   test_bit(i, chip->pull_map) ? "pull-up" :
+							 "pull-down");
+}
+
 static ssize_t gpio_sim_sysfs_val_show(struct device *dev,
 				       struct device_attribute *attr, char *buf)
 {
@@ -460,6 +481,7 @@ static int gpio_sim_add_bank(struct fwnode_handle *swnode, struct device *dev)
 	gc->to_irq = gpio_sim_to_irq;
 	gc->request = gpio_sim_request;
 	gc->free = gpio_sim_free;
+	gc->dbg_show = PTR_IF(IS_ENABLED(CONFIG_DEBUG_FS), gpio_sim_dbg_show);
 	gc->can_sleep = true;
 
 	ret = devm_gpiochip_add_data(dev, gc, chip);