[PATCH v2] staging: most: aim-cdev: make syscall write accept buffers of arbitrary size

[Christian Gromm]

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: Christian Gromm <christian.gromm at microchip.com>
---

v2: Since the previous patch of this series has beed dropped, this patch
needed some adaptation work to match the source tree again.

 drivers/staging/most/aim-cdev/cdev.c | 37 +++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/drivers/staging/most/aim-cdev/cdev.c b/drivers/staging/most/aim-cdev/cdev.c
index 5458fb9..7f51024 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;
 }
 
@@ -184,8 +188,7 @@ static ssize_t aim_write(struct file *filp, const char __user *buf,
 			 size_t count, loff_t *offset)
 {
 	int ret;
-	size_t actual_len;
-	size_t max_len;
+	size_t to_copy, left;
 	struct mbo *mbo = NULL;
 	struct aim_channel *c = filp->private_data;
 
@@ -205,20 +208,24 @@ static ssize_t aim_write(struct file *filp, const char __user *buf,
 		goto unlock;
 	}
 
-	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)) {
+	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) {
 		ret = -EFAULT;
-		goto put_mbo;
+		goto unlock;
 	}
 
-	most_submit_mbo(mbo);
-	mutex_unlock(&c->io_mutex);
-	return actual_len;
-put_mbo:
-	most_put_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);
+	}
+
+	ret = to_copy - left;
 unlock:
 	mutex_unlock(&c->io_mutex);
 	return ret;
@@ -287,7 +294,7 @@ 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