cdc_ncm: Set NTB format again after altsetting switch for Huawei devices

Some firmwares in Huawei E3372H devices have been observed to switch back
to NTB 32-bit format after altsetting switch.
This patch implements a driver flag to check for the device settings and
set NTB format to 16-bit again if needed.
The flag has been activated for devices controlled by the huawei_cdc_ncm.c
driver.

V1->V2:
- fixed broken error checks
- some corrections to the commit message
V2->V3:
- variable name changes, to clarify what's happening
- check (and possibly set) the NTB format later in the common bind code path

Signed-off-by: Enrico Mioso <mrkiko.rs@gmail.com>
Reported-and-tested-by: Christian Panton <christian@panton.org>
Reviewed-by: Bjørn Mork <bjorn@mork.no>
CC: Bjørn Mork <bjorn@mork.no>
CC: Christian Panton <christian@panton.org>
CC: linux-usb@vger.kernel.org
CC: netdev@vger.kernel.org
CC: Oliver Neukum <oliver@neukum.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/cdc_ncm.c

@@ -768,8 +768,10 @@ int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_
 	u8 *buf;
 	int len;
 	int temp;
+	int err;
 	u8 iface_no;
 	struct usb_cdc_parsed_header hdr;
+	u16 curr_ntb_format;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
@@ -874,6 +876,32 @@ int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_
 		goto error2;
 	}
 
+	/*
+	 * Some Huawei devices have been observed to come out of reset in NDP32 mode.
+	 * Let's check if this is the case, and set the device to NDP16 mode again if
+	 * needed.
+	*/
+	if (ctx->drvflags & CDC_NCM_FLAG_RESET_NTB16) {
+		err = usbnet_read_cmd(dev, USB_CDC_GET_NTB_FORMAT,
+				      USB_TYPE_CLASS | USB_DIR_IN | USB_RECIP_INTERFACE,
+				      0, iface_no, &curr_ntb_format, 2);
+		if (err < 0) {
+			goto error2;
+		}
+
+		if (curr_ntb_format == USB_CDC_NCM_NTB32_FORMAT) {
+			dev_info(&intf->dev, "resetting NTB format to 16-bit");
+			err = usbnet_write_cmd(dev, USB_CDC_SET_NTB_FORMAT,
+					       USB_TYPE_CLASS | USB_DIR_OUT
+					       | USB_RECIP_INTERFACE,
+					       USB_CDC_NCM_NTB16_FORMAT,
+					       iface_no, NULL, 0);
+
+			if (err < 0)
+				goto error2;
+		}
+	}
+
 	cdc_ncm_find_endpoints(dev, ctx->data);
 	cdc_ncm_find_endpoints(dev, ctx->control);
 	if (!dev->in || !dev->out || !dev->status) {

drivers/net/usb/huawei_cdc_ncm.c

@@ -80,6 +80,12 @@ static int huawei_cdc_ncm_bind(struct usbnet *usbnet_dev,
 	 * be at the end of the frame.
 	 */
 	drvflags |= CDC_NCM_FLAG_NDP_TO_END;
+
+	/* Additionally, it has been reported that some Huawei E3372H devices, with
+	 * firmware version 21.318.01.00.541, come out of reset in NTB32 format mode, hence
+	 * needing to be set to the NTB16 one again.
+	 */
+	drvflags |= CDC_NCM_FLAG_RESET_NTB16;
 	ret = cdc_ncm_bind_common(usbnet_dev, intf, 1, drvflags);
 	if (ret)
 		goto err;

include/linux/usb/cdc_ncm.h

@@ -83,6 +83,7 @@
 /* Driver flags */
 #define CDC_NCM_FLAG_NDP_TO_END			0x02	/* NDP is placed at end of frame */
 #define CDC_MBIM_FLAG_AVOID_ALTSETTING_TOGGLE	0x04	/* Avoid altsetting toggle during init */
+#define CDC_NCM_FLAG_RESET_NTB16 0x08	/* set NDP16 one more time after altsetting switch */
 
 #define cdc_ncm_comm_intf_is_mbim(x)  ((x)->desc.bInterfaceSubClass == USB_CDC_SUBCLASS_MBIM && \
 				       (x)->desc.bInterfaceProtocol == USB_CDC_PROTO_NONE)