1 files changed, 66 insertions, 3 deletions

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index cc0ed29a4adc..ca5d5f564998 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -103,6 +103,16 @@ static inline struct f_ncm *func_to_ncm(struct usb_function *f)
 /* Delay for the transmit to wait before sending an unfilled NTB frame. */
 #define TX_TIMEOUT_NSECS	300000
 
+/*
+ * Although max mtu as dictated by u_ether is 15412 bytes, setting
+ * max_segment_size to 15426 would not be efficient. If user chooses segment
+ * size to be (>= 8192), then we can't aggregate more than one buffer in each
+ * NTB (assuming each packet coming from network layer is >= 8192 bytes) as ep
+ * maxpacket limit is 16384. So let max_segment_size be limited to 8000 to allow
+ * at least 2 packets to be aggregated reducing wastage of NTB buffer space
+ */
+#define MAX_DATAGRAM_SIZE	8000
+
 #define FORMATS_SUPPORTED	(USB_CDC_NCM_NTB16_SUPPORTED |	\
 				 USB_CDC_NCM_NTB32_SUPPORTED)
 
@@ -179,7 +189,6 @@ static struct usb_cdc_ether_desc ecm_desc = {
 	/* this descriptor actually adds value, surprise! */
 	/* .iMACAddress = DYNAMIC */
 	.bmEthernetStatistics =	cpu_to_le32(0), /* no statistics */
-	.wMaxSegmentSize =	cpu_to_le16(ETH_FRAME_LEN),
 	.wNumberMCFilters =	cpu_to_le16(0),
 	.bNumberPowerFilters =	0,
 };
@@ -1166,11 +1175,15 @@ static int ncm_unwrap_ntb(struct gether *port,
 	struct sk_buff	*skb2;
 	int		ret = -EINVAL;
 	unsigned	ntb_max = le32_to_cpu(ntb_parameters.dwNtbOutMaxSize);
-	unsigned	frame_max = le16_to_cpu(ecm_desc.wMaxSegmentSize);
+	unsigned	frame_max;
 	const struct ndp_parser_opts *opts = ncm->parser_opts;
 	unsigned	crc_len = ncm->is_crc ? sizeof(uint32_t) : 0;
 	int		dgram_counter;
 	int		to_process = skb->len;
+	struct f_ncm_opts *ncm_opts;
+
+	ncm_opts = container_of(port->func.fi, struct f_ncm_opts, func_inst);
+	frame_max = ncm_opts->max_segment_size;
 
 parse_ntb:
 	tmp = (__le16 *)ntb_ptr;
@@ -1430,8 +1443,10 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 
 	mutex_lock(&ncm_opts->lock);
 	gether_set_gadget(ncm_opts->net, cdev->gadget);
-	if (!ncm_opts->bound)
+	if (!ncm_opts->bound) {
+		ncm_opts->net->mtu = (ncm_opts->max_segment_size - ETH_HLEN);
 		status = gether_register_netdev(ncm_opts->net);
+	}
 	mutex_unlock(&ncm_opts->lock);
 
 	if (status)
@@ -1474,6 +1489,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 	ncm_data_intf.bInterfaceNumber = status;
 	ncm_union_desc.bSlaveInterface0 = status;
 
+	ecm_desc.wMaxSegmentSize = cpu_to_le16(ncm_opts->max_segment_size);
+
 	status = -ENODEV;
 
 	/* allocate instance-specific endpoints */
@@ -1576,11 +1593,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
 /* f_ncm_opts_ifname */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
 
+static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
+					      char *page)
+{
+	struct f_ncm_opts *opts = to_f_ncm_opts(item);
+	u16 segment_size;
+
+	mutex_lock(&opts->lock);
+	segment_size = opts->max_segment_size;
+	mutex_unlock(&opts->lock);
+
+	return sysfs_emit(page, "%u\n", segment_size);
+}
+
+static ssize_t ncm_opts_max_segment_size_store(struct config_item *item,
+					       const char *page, size_t len)
+{
+	struct f_ncm_opts *opts = to_f_ncm_opts(item);
+	u16 segment_size;
+	int ret;
+
+	mutex_lock(&opts->lock);
+	if (opts->refcnt) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	ret = kstrtou16(page, 0, &segment_size);
+	if (ret)
+		goto out;
+
+	if (segment_size > MAX_DATAGRAM_SIZE) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	opts->max_segment_size = segment_size;
+	ret = len;
+out:
+	mutex_unlock(&opts->lock);
+	return ret;
+}
+
+CONFIGFS_ATTR(ncm_opts_, max_segment_size);
+
 static struct configfs_attribute *ncm_attrs[] = {
 	&ncm_opts_attr_dev_addr,
 	&ncm_opts_attr_host_addr,
 	&ncm_opts_attr_qmult,
 	&ncm_opts_attr_ifname,
+	&ncm_opts_attr_max_segment_size,
 	NULL,
 };
 
@@ -1623,6 +1685,7 @@ static struct usb_function_instance *ncm_alloc_inst(void)
 		kfree(opts);
 		return ERR_CAST(net);
 	}
+	opts->max_segment_size = ETH_FRAME_LEN;
 	INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
 
 	descs[0] = &opts->ncm_os_desc;