[RFC PATCH v1 02/20] gpio: Add GPIO polling interface to GPIO lib

[lakshmi.sowjanya.d@xxxxxxxxx]

From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>

Some Intel Timed I/O devices do not implement IRQ functionality. Augment
read() interface to allow polling.

Add two GPIO device methods: setup_poll() and poll():
- setup_poll() configures the GPIO interface e.g. capture rising edges
- poll() checks for events on the interface

To implement polling, the driver must implement the two functions above
and should either leave to_irq() method NULL or return irq 0.

setup_poll() should configure the hardware to 'listen' for input events.

poll() driver implementation must return the realtime timestamp
corresponding to the event and -EAGAIN if no data is available.

Co-developed-by: Christopher Hall <christopher.s.hall@xxxxxxxxx>
Signed-off-by: Christopher Hall <christopher.s.hall@xxxxxxxxx>
Signed-off-by: Tamal Saha <tamal.saha@xxxxxxxxx>
Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
Reviewed-by: Mark Gross <mgross@xxxxxxxxxxxxxxx>
---
 drivers/gpio/gpiolib-cdev.c | 28 ++++++++++++++++++++++++++--
 include/linux/gpio/driver.h | 19 +++++++++++++++++++
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index c7b5446d01fd..4741bf34750b 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -1227,13 +1227,34 @@ static ssize_t linereq_read(struct file *file,
 			    loff_t *f_ps)
 {
 	struct linereq *lr = file->private_data;
+	struct gpioevent_poll_data poll_data;
 	struct gpio_v2_line_event le;
 	ssize_t bytes_read = 0;
-	int ret;
+	int ret, offset;
 
 	if (count < sizeof(le))
 		return -EINVAL;
 
+	/* Without an IRQ, we can only poll */
+	offset = gpio_chip_hwgpio(lr->gdev->descs);
+	if (lr->lines[offset].irq == 0) {
+		struct gpio_v2_line_event *event;
+
+		if (!(file->f_flags & O_NONBLOCK))
+			return -ENODEV;
+
+		ret = lr->gdev->chip->do_poll(lr->gdev->chip, offset,
+					      lr->lines[offset].eflags, &poll_data);
+		if (ret)
+			return ret;
+		event = kzalloc(sizeof(*event), GFP_KERNEL);
+		event->timestamp_ns = poll_data.timestamp;
+		event->id = poll_data.id;
+		if (copy_to_user(buf, (void *)&event, sizeof(event)))
+			return -EFAULT;
+		return sizeof(event);
+	}
+
 	do {
 		spin_lock(&lr->wait.lock);
 		if (kfifo_is_empty(&lr->events)) {
@@ -1314,6 +1335,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 {
 	struct gpio_v2_line_request ulr;
 	struct gpio_v2_line_config *lc;
+	unsigned int file_flags;
 	struct linereq *lr;
 	struct file *file;
 	u64 flags;
@@ -1411,6 +1433,8 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 				goto out_free_linereq;
 		}
 
+		file_flags = O_RDONLY | O_CLOEXEC;
+
 		blocking_notifier_call_chain(&desc->gdev->notifier,
 					     GPIO_V2_LINE_CHANGED_REQUESTED, desc);
 
@@ -1425,7 +1449,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 	}
 
 	file = anon_inode_getfile("gpio-line", &line_fileops, lr,
-				  O_RDONLY | O_CLOEXEC);
+				  file_flags);
 	if (IS_ERR(file)) {
 		ret = PTR_ERR(file);
 		goto out_put_unused_fd;
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 3a268781fcec..f5b971ad40bc 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -17,6 +17,7 @@ struct device_node;
 struct seq_file;
 struct gpio_device;
 struct module;
+struct gpioevent_poll_data;
 enum gpiod_flags;
 enum gpio_lookup_flags;
 
@@ -304,6 +305,11 @@ struct gpio_irq_chip {
  * @add_pin_ranges: optional routine to initialize pin ranges, to be used when
  *	requires special mapping of the pins that provides GPIO functionality.
  *	It is called after adding GPIO chip and before adding IRQ chip.
+ * @setup_poll: optional routine for devices that don't support interrupts.
+ *	Takes flags argument as in/out parameter, where caller requests
+ *	event flags and driver returns accepted flags.
+ * @do_poll: optional routine for devices that don't support interrupts.
+ *	Returns event specification in data parameter.
  * @base: identifies the first GPIO number handled by this chip;
  *	or, if negative during registration, requests dynamic ID allocation.
  *	DEPRECATION: providing anything non-negative and nailing the base
@@ -396,6 +402,14 @@ struct gpio_chip {
 
 	int			(*add_pin_ranges)(struct gpio_chip *gc);
 
+	int                     (*setup_poll)(struct gpio_chip *chip,
+					      unsigned int offset,
+					      u32 *eflags);
+
+	int                     (*do_poll)(struct gpio_chip *chip,
+					   unsigned int offset, u32 eflags,
+					   struct gpioevent_poll_data *data);
+
 	int			base;
 	u16			ngpio;
 	const char		*const *names;
@@ -471,6 +485,11 @@ struct gpio_chip {
 #endif /* CONFIG_OF_GPIO */
 };
 
+struct gpioevent_poll_data {
+	__u64 timestamp;
+	__u32 id;
+};
+
 extern const char *gpiochip_is_requested(struct gpio_chip *gc,
 			unsigned int offset);
 
-- 
2.17.1