gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL

Add support for GPIO_V2_LINE_SET_CONFIG_IOCTL, the uAPI v2
line set config ioctl.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpiolib-cdev.c

@@ -16,6 +16,7 @@
 #include <linux/kernel.h>
 #include <linux/kfifo.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/poll.h>
 #include <linux/spinlock.h>
@@ -444,6 +445,8 @@ struct line {
  * @seqno: the sequence number for edge events generated on all lines in
  * this line request.  Note that this is not used when @num_lines is 1, as
  * the line_seqno is then the same and is cheaper to calculate.
+ * @config_mutex: mutex for serializing ioctl() calls to ensure consistency
+ * of configuration, particularly multi-step accesses to desc flags.
  * @lines: the lines held by this line request, with @num_lines elements.
  */
 struct linereq {
@@ -454,6 +457,7 @@ struct linereq {
 	u32 event_buffer_size;
 	DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
 	atomic_t seqno;
+	struct mutex config_mutex;
 	struct line lines[];
 };
 
@@ -574,6 +578,8 @@ static void edge_detector_stop(struct line *line)
 		free_irq(line->irq, line);
 		line->irq = 0;
 	}
+
+	line->eflags = 0;
 }
 
 static int edge_detector_setup(struct line *line,
@@ -615,6 +621,17 @@ static int edge_detector_setup(struct line *line,
 	return 0;
 }
 
+static int edge_detector_update(struct line *line, u64 eflags,
+				bool polarity_change)
+{
+	if ((line->eflags == eflags) && !polarity_change)
+		return 0;
+
+	edge_detector_stop(line);
+
+	return edge_detector_setup(line, eflags);
+}
+
 static u64 gpio_v2_line_config_flags(struct gpio_v2_line_config *lc,
 				     unsigned int line_idx)
 {
@@ -799,6 +816,74 @@ static long linereq_get_values(struct linereq *lr, void __user *ip)
 	return 0;
 }
 
+static long linereq_set_config_unlocked(struct linereq *lr,
+					struct gpio_v2_line_config *lc)
+{
+	struct gpio_desc *desc;
+	unsigned int i;
+	u64 flags;
+	bool polarity_change;
+	int ret;
+
+	for (i = 0; i < lr->num_lines; i++) {
+		desc = lr->lines[i].desc;
+		flags = gpio_v2_line_config_flags(lc, i);
+		polarity_change =
+			(!!test_bit(FLAG_ACTIVE_LOW, &desc->flags) !=
+			 ((flags & GPIO_V2_LINE_FLAG_ACTIVE_LOW) != 0));
+
+		gpio_v2_line_config_flags_to_desc_flags(flags, &desc->flags);
+		/*
+		 * Lines have to be requested explicitly for input
+		 * or output, else the line will be treated "as is".
+		 */
+		if (flags & GPIO_V2_LINE_FLAG_OUTPUT) {
+			int val = gpio_v2_line_config_output_value(lc, i);
+
+			edge_detector_stop(&lr->lines[i]);
+			ret = gpiod_direction_output(desc, val);
+			if (ret)
+				return ret;
+		} else if (flags & GPIO_V2_LINE_FLAG_INPUT) {
+			ret = gpiod_direction_input(desc);
+			if (ret)
+				return ret;
+
+			ret = edge_detector_update(&lr->lines[i],
+					flags & GPIO_V2_LINE_EDGE_FLAGS,
+					polarity_change);
+			if (ret)
+				return ret;
+		}
+
+		blocking_notifier_call_chain(&desc->gdev->notifier,
+					     GPIO_V2_LINE_CHANGED_CONFIG,
+					     desc);
+	}
+	return 0;
+}
+
+static long linereq_set_config(struct linereq *lr, void __user *ip)
+{
+	struct gpio_v2_line_config lc;
+	int ret;
+
+	if (copy_from_user(&lc, ip, sizeof(lc)))
+		return -EFAULT;
+
+	ret = gpio_v2_line_config_validate(&lc, lr->num_lines);
+	if (ret)
+		return ret;
+
+	mutex_lock(&lr->config_mutex);
+
+	ret = linereq_set_config_unlocked(lr, &lc);
+
+	mutex_unlock(&lr->config_mutex);
+
+	return ret;
+}
+
 static long linereq_ioctl(struct file *file, unsigned int cmd,
 			  unsigned long arg)
 {
@@ -807,6 +892,8 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
 
 	if (cmd == GPIO_V2_LINE_GET_VALUES_IOCTL)
 		return linereq_get_values(lr, ip);
+	else if (cmd == GPIO_V2_LINE_SET_CONFIG_IOCTL)
+		return linereq_set_config(lr, ip);
 
 	return -EINVAL;
 }
@@ -968,6 +1055,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 		}
 	}
 
+	mutex_init(&lr->config_mutex);
 	init_waitqueue_head(&lr->wait);
 	lr->event_buffer_size = ulr.event_buffer_size;
 	if (lr->event_buffer_size == 0)