RFC: [PATCH 1/3] usb: cdc_ncm: patch for VMware

[Loic Domaigne <loic.domaigne@googlemail.com>]

This patch limits the Rx URB size to 16kB if the driver is compiled for a
VMware environment. As of workstation 9, there are some major performance
problems if the Rx URB size exceeds that limit.

This patch applies to longterm kernel version 3.4.35.

Signed-Off-By: Loic Domaigne <loic.domaigne@jambit.com> 

--- linux-3.4.35/drivers/net/usb/cdc_ncm.c.orig	2013-03-05 09:36:02.858740489 +0100
+++ linux-3.4.35/drivers/net/usb/cdc_ncm.c	2013-03-05 10:20:18.092588668 +0100
@@ -80,6 +80,23 @@
 #define	CDC_NCM_TIMER_PENDING_CNT		2
 #define CDC_NCM_TIMER_INTERVAL			(400UL * NSEC_PER_USEC)
 
+/* maximum Rx URB size */
+/*
+ * in the original Linux driver, the rx urb size can be up to
+ * CDC_NCM_NTB_MAX_SIZE_RX.
+ *
+ * Under VMware (as of wks9), URB size greater than 16kB is a problem,
+ * so simply adjust this define when the driver is compiled for a VMware
+ * environment.
+ *
+ */
+#ifdef VMWARE_BUG
+#warning "Compiling for VMware"
+#define CDC_NCM_MAX_RX_URB_SIZE     16384
+#else
+#define CDC_NCM_MAX_RX_URB_SIZE     CDC_NCM_NTB_MAX_SIZE_RX
+#endif
+
 /* The following macro defines the minimum header space */
 #define	CDC_NCM_MIN_HDR_SIZE \
 	(sizeof(struct usb_cdc_ncm_nth16) + sizeof(struct usb_cdc_ncm_ndp16) + \
@@ -589,6 +606,9 @@ advance:
 		ctx->out_ep->desc.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
 	dev->status = ctx->status_ep;
 	dev->rx_urb_size = ctx->rx_max;
+	if (dev->rx_urb_size > CDC_NCM_MAX_RX_URB_SIZE)
+		dev->rx_urb_size = CDC_NCM_MAX_RX_URB_SIZE;
+	pr_debug("dev->rx_urb_size = %zu", dev->rx_urb_size);
 
 	/*
 	 * We should get an event when network connection is "connected" or