[PATCH 2/4] rpmsg: char: Add support to use rpmsg_rx_done

[Chris Lew <quic_clew@quicinc.com>]

Add support into the rpmsg char driver to skip copying the data into an
skb if the endpoint supports rpmsg_rx_done. If the endpoint supports
the rx_done operation, allocate a zero sized skb and set the data to
the buffer returned in the rx callback. When the packet is read from
the character device, release the memory by calling rpmsg_rx_done().

Signed-off-by: Chris Lew <quic_clew@quicinc.com>
---
 drivers/rpmsg/rpmsg_char.c | 50 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index b6183d4f62a2..be62ddcf356c 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -91,8 +91,8 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
 }
 EXPORT_SYMBOL(rpmsg_chrdev_eptdev_destroy);
 
-static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
-			void *priv, u32 addr)
+static int rpmsg_ept_copy_cb(struct rpmsg_device *rpdev, void *buf, int len,
+			     void *priv, u32 addr)
 {
 	struct rpmsg_eptdev *eptdev = priv;
 	struct sk_buff *skb;
@@ -113,6 +113,43 @@ static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
 	return 0;
 }
 
+static int rpmsg_ept_no_copy_cb(struct rpmsg_device *rpdev, void *buf, int len,
+				void *priv, u32 addr)
+{
+	struct rpmsg_eptdev *eptdev = priv;
+	struct sk_buff *skb;
+
+	skb = alloc_skb(0, GFP_ATOMIC);
+	if (!skb)
+		return -ENOMEM;
+
+	skb->head = buf;
+	skb->data = buf;
+	skb_reset_tail_pointer(skb);
+	skb_set_end_offset(skb, len);
+	skb_put(skb, len);
+
+	spin_lock(&eptdev->queue_lock);
+	skb_queue_tail(&eptdev->queue, skb);
+	spin_unlock(&eptdev->queue_lock);
+
+	/* wake up any blocking processes, waiting for new data */
+	wake_up_interruptible(&eptdev->readq);
+
+	return RPMSG_DEFER;
+}
+
+static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
+			void *priv, u32 addr)
+{
+	struct rpmsg_eptdev *eptdev = priv;
+	rpmsg_rx_cb_t cb;
+
+	cb = (eptdev->ept->rx_done) ? rpmsg_ept_no_copy_cb : rpmsg_ept_copy_cb;
+
+	return cb(rpdev, buf, len, priv, addr);
+}
+
 static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
 {
 	struct rpmsg_eptdev *eptdev = cdev_to_eptdev(inode->i_cdev);
@@ -210,6 +247,15 @@ static ssize_t rpmsg_eptdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	if (copy_to_iter(skb->data, use, to) != use)
 		use = -EFAULT;
 
+	if (eptdev->ept->rx_done) {
+		rpmsg_rx_done(eptdev->ept, skb->data);
+		/*
+		 * Data memory is freed by rpmsg_rx_done(), reset the skb data
+		 * pointers so kfree_skb() does not try to free a second time.
+		 */
+		skb->head = NULL;
+		skb->data = NULL;
+	}
 	kfree_skb(skb);
 
 	return use;
-- 
2.7.4