Enlarge USB bulk transfer size for faster downloads

The default USB transfer bulk is fixed as 4096 in fastboot util code for
Windows and Linux. Enlarging the bulk size can greatly improve the image
download speed via USB.

For Windows, adjust the max bulk size to 1MB to maximize the USB transfer
speed. With this change, the USB transfer speed can be doubled to 20MB/s.

For Linux, adjust the max bulk size to 16384 to maximize the USB transfer
speed according to MAX_USBFS_BUFFER_SIZE definition in drivers/usb/core/devio.c.

For OSX, the maxLenToSend is already 1MB in code.

Change-Id: If6af8c6301f6f6c2ef345e37241706f16d8f5cda

fastboot/usb_linux.c

@@ -61,6 +61,11 @@
 #define DBG1(x...)
 #endif
 
+/* The max bulk size for linux is 16384 which is defined
+ * in drivers/usb/core/devio.c.
+ */
+#define MAX_USBFS_BULK_SIZE (16 * 1024)
+
 struct usb_handle 
 {
     char fname[64];
@@ -289,7 +294,7 @@ int usb_write(usb_handle *h, const void *_data, int len)
 
     while(len > 0) {
         int xfer;
-        xfer = (len > 4096) ? 4096 : len;
+        xfer = (len > MAX_USBFS_BULK_SIZE) ? MAX_USBFS_BULK_SIZE : len;
 
         bulk.ep = h->ep_out;
         bulk.len = xfer;
@@ -323,7 +328,7 @@ int usb_read(usb_handle *h, void *_data, int len)
     }
 
     while(len > 0) {
-        int xfer = (len > 4096) ? 4096 : len;
+        int xfer = (len > MAX_USBFS_BULK_SIZE) ? MAX_USBFS_BULK_SIZE : len;
 
         bulk.ep = h->ep_in;
         bulk.len = xfer;

fastboot/usb_windows.c

@@ -42,6 +42,7 @@
 #define DBG(x...)
 #endif
 
+#define MAX_USBFS_BULK_SIZE (1024 * 1024)
 
 /** Structure usb_handle describes our connection to the usb device via
   AdbWinApi.dll. This structure is returned from usb_open() routine and
@@ -160,7 +161,7 @@ int usb_write(usb_handle* handle, const void* data, int len) {
     if (NULL != handle) {
         // Perform write
         while(len > 0) {
-            int xfer = (len > 4096) ? 4096 : len;
+            int xfer = (len > MAX_USBFS_BULK_SIZE) ? MAX_USBFS_BULK_SIZE : len;
             ret = AdbWriteEndpointSync(handle->adb_write_pipe,
                                    (void*)data,
                                    (unsigned long)xfer,
@@ -200,7 +201,7 @@ int usb_read(usb_handle *handle, void* data, int len) {
     DBG("usb_read %d\n", len);
     if (NULL != handle) {
         while (1) {
-            int xfer = (len > 4096) ? 4096 : len;
+            int xfer = (len > MAX_USBFS_BULK_SIZE) ? MAX_USBFS_BULK_SIZE : len;
 
 	        ret = AdbReadEndpointSync(handle->adb_read_pipe,
 	                              (void*)data,