staging: most: usb: fix calculation of the extra_len

The final size of the buffer used for the streaming transfer consists of
the size for the user payload (buffer_size) and the size for the gaps
needed by the controller (extra_len).

The current implementation of the hdm_configure_channel() corrects the
buffer size down to the next appropriate for the hardware value, that is
the whole number of frames, but uses the old unaligned value to
calculate the extra_len.

Current patch fixes the described problem.
Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/hdm-usb/hdm_usb.c

@@ -649,8 +649,6 @@ static int hdm_configure_channel(struct most_interface *iface, int channel,
 {
 	unsigned int num_frames;
 	unsigned int frame_size;
-	unsigned int temp_size;
-	unsigned int tail_space;
 	struct most_dev *mdev = to_mdev(iface);
 	struct device *dev = &mdev->usb_device->dev;
 
@@ -685,7 +683,6 @@ static int hdm_configure_channel(struct most_interface *iface, int channel,
 	}
 
 	mdev->padding_active[channel] = true;
-	temp_size = conf->buffer_size;
 
 	frame_size = get_stream_frame_size(conf);
 	if (frame_size == 0 || frame_size > USB_MTU) {
@@ -693,25 +690,19 @@ static int hdm_configure_channel(struct most_interface *iface, int channel,
 		return -EINVAL;
 	}
 
+	num_frames = conf->buffer_size / frame_size;
+
 	if (conf->buffer_size % frame_size) {
-		u16 tmp_val;
-
-		tmp_val = conf->buffer_size / frame_size;
-		conf->buffer_size = tmp_val * frame_size;
-		dev_notice(dev,
-			   "Channel %d - rounding buffer size to %d bytes, channel config says %d bytes\n",
-			   channel,
-			   conf->buffer_size,
-			   temp_size);
-	}
+		u16 old_size = conf->buffer_size;
 
-	num_frames = conf->buffer_size / frame_size;
-	tail_space = num_frames * (USB_MTU - frame_size);
-	temp_size += tail_space;
+		conf->buffer_size = num_frames * frame_size;
+		dev_warn(dev, "%s: fixed buffer size (%d -> %d)\n",
+			 mdev->suffix[channel], old_size, conf->buffer_size);
+	}
 
 	/* calculate extra length to comply w/ HW padding */
-	conf->extra_len = (DIV_ROUND_UP(temp_size, USB_MTU) * USB_MTU)
-			  - conf->buffer_size;
+	conf->extra_len = num_frames * (USB_MTU - frame_size);
+
 exit:
 	mdev->conf[channel] = *conf;
 	if (conf->data_type == MOST_CH_ASYNC) {