platform/chrome: cros_ec_chardev: Add a poll handler to receive MKBP events

Allow to poll on the cros_ec device to receive the MKBP events.

The /dev/cros_[ec|fp|..] file operations now implements the poll
operation. The userspace can now receive specific MKBP events by doing
the following:

- Open the /dev/cros_XX file.
- Call the CROS_EC_DEV_IOCEVENTMASK ioctl with the bitmap of the MKBP
  events it wishes to receive as argument.
- Poll on the file descriptor.
- When it gets POLLIN, do a read on the file descriptor, the first
  queued event will be returned (using the struct
  ec_response_get_next_event format: one byte of event type, then
  the payload).

The read() operation returns at most one event even if there are several
queued, and it might be truncated if the buffer is smaller than the
event (but the caller should know the maximum size of the events it is
reading).

read() used to return the EC version string, it still does it when no
event mask or an empty event is set for backward compatibility (despite
nobody really using this feature).

This will be used, for example, by the userspace daemon to receive and
treat the EC_MKBP_EVENT_FINGERPRINT sent by the FP MCU.
Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>

drivers/platform/chrome/cros_ec_chardev.c

@@ -16,21 +16,42 @@
 #include <linux/mfd/cros_ec.h>
 #include <linux/miscdevice.h>
 #include <linux/module.h>
+#include <linux/notifier.h>
 #include <linux/platform_data/cros_ec_chardev.h>
 #include <linux/platform_data/cros_ec_commands.h>
 #include <linux/platform_data/cros_ec_proto.h>
 #include <linux/platform_device.h>
+#include <linux/poll.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
 
 #define DRV_NAME		"cros-ec-chardev"
 
+/* Arbitrary bounded size for the event queue */
+#define CROS_MAX_EVENT_LEN	PAGE_SIZE
+
 struct chardev_data {
 	struct cros_ec_dev *ec_dev;
 	struct miscdevice misc;
 };
 
+struct chardev_priv {
+	struct cros_ec_dev *ec_dev;
+	struct notifier_block notifier;
+	wait_queue_head_t wait_event;
+	unsigned long event_mask;
+	struct list_head events;
+	size_t event_len;
+};
+
+struct ec_event {
+	struct list_head node;
+	size_t size;
+	u8 event_type;
+	u8 data[0];
+};
+
 static int ec_get_version(struct cros_ec_dev *ec, char *str, int maxlen)
 {
 	static const char * const current_image_name[] = {
@@ -69,6 +90,71 @@ static int ec_get_version(struct cros_ec_dev *ec, char *str, int maxlen)
 	return ret;
 }
 
+static int cros_ec_chardev_mkbp_event(struct notifier_block *nb,
+				      unsigned long queued_during_suspend,
+				      void *_notify)
+{
+	struct chardev_priv *priv = container_of(nb, struct chardev_priv,
+						 notifier);
+	struct cros_ec_device *ec_dev = priv->ec_dev->ec_dev;
+	struct ec_event *event;
+	unsigned long event_bit = 1 << ec_dev->event_data.event_type;
+	int total_size = sizeof(*event) + ec_dev->event_size;
+
+	if (!(event_bit & priv->event_mask) ||
+	    (priv->event_len + total_size) > CROS_MAX_EVENT_LEN)
+		return NOTIFY_DONE;
+
+	event = kzalloc(total_size, GFP_KERNEL);
+	if (!event)
+		return NOTIFY_DONE;
+
+	event->size = ec_dev->event_size;
+	event->event_type = ec_dev->event_data.event_type;
+	memcpy(event->data, &ec_dev->event_data.data, ec_dev->event_size);
+
+	spin_lock(&priv->wait_event.lock);
+	list_add_tail(&event->node, &priv->events);
+	priv->event_len += total_size;
+	wake_up_locked(&priv->wait_event);
+	spin_unlock(&priv->wait_event.lock);
+
+	return NOTIFY_OK;
+}
+
+static struct ec_event *cros_ec_chardev_fetch_event(struct chardev_priv *priv,
+						    bool fetch, bool block)
+{
+	struct ec_event *event;
+	int err;
+
+	spin_lock(&priv->wait_event.lock);
+	if (!block && list_empty(&priv->events)) {
+		event = ERR_PTR(-EWOULDBLOCK);
+		goto out;
+	}
+
+	if (!fetch) {
+		event = NULL;
+		goto out;
+	}
+
+	err = wait_event_interruptible_locked(priv->wait_event,
+					      !list_empty(&priv->events));
+	if (err) {
+		event = ERR_PTR(err);
+		goto out;
+	}
+
+	event = list_first_entry(&priv->events, struct ec_event, node);
+	list_del(&event->node);
+	priv->event_len -= sizeof(*event) + event->size;
+
+out:
+	spin_unlock(&priv->wait_event.lock);
+	return event;
+}
+
 /*
  * Device file ops
  */
@@ -76,11 +162,40 @@ static int cros_ec_chardev_open(struct inode *inode, struct file *filp)
 {
 	struct miscdevice *mdev = filp->private_data;
 	struct cros_ec_dev *ec_dev = dev_get_drvdata(mdev->parent);
+	struct chardev_priv *priv;
+	int ret;
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
 
-	filp->private_data = ec_dev;
+	priv->ec_dev = ec_dev;
+	filp->private_data = priv;
+	INIT_LIST_HEAD(&priv->events);
+	init_waitqueue_head(&priv->wait_event);
 	nonseekable_open(inode, filp);
 
+	priv->notifier.notifier_call = cros_ec_chardev_mkbp_event;
+	ret = blocking_notifier_chain_register(&ec_dev->ec_dev->event_notifier,
+					       &priv->notifier);
+	if (ret) {
+		dev_err(ec_dev->dev, "failed to register event notifier\n");
+		kfree(priv);
+	}
+
+	return ret;
+}
+
+static __poll_t cros_ec_chardev_poll(struct file *filp, poll_table *wait)
+{
+	struct chardev_priv *priv = filp->private_data;
+
+	poll_wait(filp, &priv->wait_event, wait);
+
+	if (list_empty(&priv->events))
 		return 0;
+
+	return EPOLLIN | EPOLLRDNORM;
 }
 
 static ssize_t cros_ec_chardev_read(struct file *filp, char __user *buffer,
@@ -88,14 +203,42 @@ static ssize_t cros_ec_chardev_read(struct file *filp, char __user *buffer,
 {
 	char msg[sizeof(struct ec_response_get_version) +
 		 sizeof(CROS_EC_DEV_VERSION)];
-	struct cros_ec_dev *ec = filp->private_data;
+	struct chardev_priv *priv = filp->private_data;
+	struct cros_ec_dev *ec_dev = priv->ec_dev;
 	size_t count;
 	int ret;
 
+	if (priv->event_mask) { /* queued MKBP event */
+		struct ec_event *event;
+
+		event = cros_ec_chardev_fetch_event(priv, length != 0,
+						!(filp->f_flags & O_NONBLOCK));
+		if (IS_ERR(event))
+			return PTR_ERR(event);
+		/*
+		 * length == 0 is special - no IO is done but we check
+		 * for error conditions.
+		 */
+		if (length == 0)
+			return 0;
+
+		/* The event is 1 byte of type plus the payload */
+		count = min(length, event->size + 1);
+		ret = copy_to_user(buffer, &event->event_type, count);
+		kfree(event);
+		if (ret) /* the copy failed */
+			return -EFAULT;
+		*offset = count;
+		return count;
+	}
+
+	/*
+	 * Legacy behavior if no event mask is defined
+	 */
 	if (*offset != 0)
 		return 0;
 
-	ret = ec_get_version(ec, msg, sizeof(msg));
+	ret = ec_get_version(ec_dev, msg, sizeof(msg));
 	if (ret)
 		return ret;
 
@@ -108,6 +251,24 @@ static ssize_t cros_ec_chardev_read(struct file *filp, char __user *buffer,
 	return count;
 }
 
+static int cros_ec_chardev_release(struct inode *inode, struct file *filp)
+{
+	struct chardev_priv *priv = filp->private_data;
+	struct cros_ec_dev *ec_dev = priv->ec_dev;
+	struct ec_event *event, *e;
+
+	blocking_notifier_chain_unregister(&ec_dev->ec_dev->event_notifier,
+					   &priv->notifier);
+
+	list_for_each_entry_safe(event, e, &priv->events, node) {
+		list_del(&event->node);
+		kfree(event);
+	}
+	kfree(priv);
+
+	return 0;
+}
+
 /*
  * Ioctls
  */
@@ -181,7 +342,8 @@ static long cros_ec_chardev_ioctl_readmem(struct cros_ec_dev *ec,
 static long cros_ec_chardev_ioctl(struct file *filp, unsigned int cmd,
 				   unsigned long arg)
 {
-	struct cros_ec_dev *ec = filp->private_data;
+	struct chardev_priv *priv = filp->private_data;
+	struct cros_ec_dev *ec = priv->ec_dev;
 
 	if (_IOC_TYPE(cmd) != CROS_EC_DEV_IOC)
 		return -ENOTTY;
@@ -191,6 +353,9 @@ static long cros_ec_chardev_ioctl(struct file *filp, unsigned int cmd,
 		return cros_ec_chardev_ioctl_xcmd(ec, (void __user *)arg);
 	case CROS_EC_DEV_IOCRDMEM:
 		return cros_ec_chardev_ioctl_readmem(ec, (void __user *)arg);
+	case CROS_EC_DEV_IOCEVENTMASK:
+		priv->event_mask = arg;
+		return 0;
 	}
 
 	return -ENOTTY;
@@ -198,7 +363,9 @@ static long cros_ec_chardev_ioctl(struct file *filp, unsigned int cmd,
 
 static const struct file_operations chardev_fops = {
 	.open		= cros_ec_chardev_open,
+	.poll		= cros_ec_chardev_poll,
 	.read		= cros_ec_chardev_read,
+	.release	= cros_ec_chardev_release,
 	.unlocked_ioctl	= cros_ec_chardev_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= cros_ec_chardev_ioctl,

include/linux/platform_data/cros_ec_chardev.h

@@ -33,5 +33,6 @@ struct cros_ec_readmem {
 #define CROS_EC_DEV_IOC       0xEC
 #define CROS_EC_DEV_IOCXCMD   _IOWR(CROS_EC_DEV_IOC, 0, struct cros_ec_command)
 #define CROS_EC_DEV_IOCRDMEM  _IOWR(CROS_EC_DEV_IOC, 1, struct cros_ec_readmem)
+#define CROS_EC_DEV_IOCEVENTMASK _IO(CROS_EC_DEV_IOC, 2)
 
 #endif /* _CROS_EC_DEV_H_ */