[PATCH 3/6] staging: most: aim-cdev: make syscall write accept buffers of arbitrary size

[Christian Gromm]

From: Andrey Shvetsov <andrey.shvetsov at k2l.de>

This patch allows to call the write() function for synchronous and
isochronous channels with buffers of any size. The AIM simply waits for
data to fill up the MOST buffer object according to the network interface
controller specification for streaming channels, before it submits the
buffer to the HDM.

The new behavior is backward compatible to the old applications, since
all known applications needed to fill the buffer completely anyway.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov at k2l.de>
Signed-off-by: Christian Gromm <christian.gromm at microchip.com>
---
 drivers/staging/most/aim-cdev/cdev.c | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/most/aim-cdev/cdev.c b/drivers/staging/most/aim-cdev/cdev.c
index f6a7b75..0a06d7f 100644
--- a/drivers/staging/most/aim-cdev/cdev.c
+++ b/drivers/staging/most/aim-cdev/cdev.c
@@ -57,7 +57,11 @@ static inline bool ch_has_mbo(struct aim_channel *c)
 
 static inline bool ch_get_mbo(struct aim_channel *c, struct mbo **mbo)
 {
-	*mbo = most_get_mbo(c->iface, c->channel_id, &cdev_aim);
+	if (!kfifo_peek(&c->fifo, mbo)) {
+		*mbo = most_get_mbo(c->iface, c->channel_id, &cdev_aim);
+		if (*mbo)
+			kfifo_in(&c->fifo, mbo, 1);
+	}
 	return *mbo;
 }
 
@@ -183,8 +187,7 @@ static int aim_close(struct inode *inode, struct file *filp)
 static ssize_t aim_write(struct file *filp, const char __user *buf,
 			 size_t count, loff_t *offset)
 {
-	size_t actual_len;
-	size_t max_len;
+	size_t to_copy, left;
 	struct mbo *mbo = NULL;
 	struct aim_channel *c = filp->private_data;
 
@@ -204,19 +207,25 @@ static ssize_t aim_write(struct file *filp, const char __user *buf,
 		return -ENODEV;
 	}
 
-	max_len = c->cfg->buffer_size;
-	actual_len = min(count, max_len);
-	mbo->buffer_length = actual_len;
-
-	if (copy_from_user(mbo->virt_address, buf, mbo->buffer_length)) {
-		most_put_mbo(mbo);
+	to_copy = min(count, c->cfg->buffer_size - c->mbo_offs);
+	left = copy_from_user(mbo->virt_address + c->mbo_offs, buf, to_copy);
+	if (left == to_copy) {
 		mutex_unlock(&c->io_mutex);
 		return -EFAULT;
 	}
 
-	most_submit_mbo(mbo);
+	c->mbo_offs += to_copy - left;
+	if (c->mbo_offs >= c->cfg->buffer_size ||
+	    c->cfg->data_type == MOST_CH_CONTROL ||
+	    c->cfg->data_type == MOST_CH_ASYNC) {
+		kfifo_skip(&c->fifo);
+		mbo->buffer_length = c->mbo_offs;
+		c->mbo_offs = 0;
+		most_submit_mbo(mbo);
+	}
+
 	mutex_unlock(&c->io_mutex);
-	return actual_len;
+	return to_copy - left;
 }
 
 /**
@@ -282,7 +291,7 @@ static unsigned int aim_poll(struct file *filp, poll_table *wait)
 		if (!kfifo_is_empty(&c->fifo))
 			mask |= POLLIN | POLLRDNORM;
 	} else {
-		if (ch_has_mbo(c))
+		if (!kfifo_is_empty(&c->fifo) || ch_has_mbo(c))
 			mask |= POLLOUT | POLLWRNORM;
 	}
 	return mask;
-- 
1.9.1