[U-Boot] usb_stor_BBB_transport 5 ms delay - performance

[Jim Shimer]

I'm seeing a 5ms delay in usb_stor_BBB_transport, which occurs every 10K of
data for fatload usb or 500ms of delay per 1MB of image size.  This adds up
to quite a bit of delay if you're loading a large ramdisk.

Does anyone know what the reason for the 5ms delay really is?  I'm assuming
that this delay is to debounce the 5V/100ma USB power up.  I made some
modification, where the delay is skipped if the device has already been
queried as ready.  This has save me 500ms/M on fatload times (eg,
140M=70seconds).  Is there anything wrong with this tweak?

Here's a diff of what I've done to get the performance I need:

--- usb_storage.c.orig  2012-07-26 16:06:40.775251000 -0400
+++ usb_storage.c       2012-07-26 13:49:36.000000000 -0400
@@ -132,6 +132,7 @@ static block_dev_desc_t usb_dev_desc[USB
 struct us_data;
 typedef int (*trans_cmnd)(ccb *cb, struct us_data *data);
 typedef int (*trans_reset)(struct us_data *data);
+typedef enum us_status { USB_NOT_READY, USB_READY} us_status;

 struct us_data {
        struct usb_device *pusb_dev;     /* this usb_device */
@@ -154,6 +155,7 @@ struct us_data {
        ccb             *srb;                   /* current srb */
        trans_reset     transport_reset;        /* reset routine */
        trans_cmnd      transport;              /* transport routine */
+       us_status       status;
 };

 static struct us_data usb_stor[USB_MAX_STOR_DEV];
@@ -691,7 +693,10 @@ int usb_stor_BBB_transport(ccb *srb, str
                usb_stor_BBB_reset(us);
                return USB_STOR_TRANSPORT_FAILED;
        }
-       wait_ms(5);
+       if(us->status != USB_READY)
+       {
+               wait_ms(5);
+       }
        pipein = usb_rcvbulkpipe(us->pusb_dev, us->ep_in);
        pipeout = usb_sndbulkpipe(us->pusb_dev, us->ep_out);
        /* DATA phase + error handling */
@@ -957,7 +962,10 @@ static int usb_test_unit_ready(ccb *srb,
                srb->datalen = 0;
                srb->cmdlen = 12;
                if (ss->transport(srb, ss) == USB_STOR_TRANSPORT_GOOD)
+               {
+                       ss->status = USB_READY;
                        return 0;
+               }
                usb_request_sense(srb, ss);
                wait_ms(100);
        } while (retries--);
@@ -965,6 +973,11 @@ static int usb_test_unit_ready(ccb *srb,
        return -1;
 }

+static void usb_set_unit_not_ready(struct us_data *ss)
+{
+       ss->status = USB_NOT_READY;
+}
+
 static int usb_read_capacity(ccb *srb, struct us_data *ss)
 {
        int retry;
@@ -1108,6 +1121,7 @@ retry_it:
                blks -= smallblks;
                buf_addr += srb->datalen;
        } while (blks != 0);
+       usb_set_unit_not_ready((struct us_data *)dev->privptr);

        USB_STOR_PRINTF("usb_read: end startblk %lx, blccnt %x buffer
%lx\n",
                        start, smallblks, buf_addr);
@@ -1188,6 +1202,7 @@ retry_it:
                blks -= smallblks;
                buf_addr += srb->datalen;
        } while (blks != 0);
+       usb_set_unit_not_ready((struct us_data *)dev->privptr);

        USB_STOR_PRINTF("usb_write: end startblk %lx, blccnt %x buffer
%lx\n",
                        start, smallblks, buf_addr);
@@ -1398,6 +1413,7 @@ int usb_stor_get_info(struct usb_device
                cap[0] = 2880;
                cap[1] = 0x200;
        }
+       usb_set_unit_not_ready((struct us_data *)dev->privptr);
        USB_STOR_PRINTF("Read Capacity returns: 0x%lx, 0x%lx\n", cap[0],
                        cap[1]);
 #if 0


I'd appreciate any feedback.
Regards

-- 
*James H Shimer*
Motorola Mobility T3-12-HH72
900 Chelmsford Street
Lowell MA 08151
978-614-3550