ChangeSet 1.1557.49.10, 2004/02/17 16:43:54-08:00, [EMAIL PROTECTED]
[PATCH] USB Storage: Handle excess 0-length data packets
This patch is an attempt to cope with Genesys Logic's, shall we say,
creative approach to implementing the USB protocols. Their high-speed
mass storage devices sometimes add an excess 0-length packet to the end of
a data phase transmission. Of course we don't read that packet as part of
the data phase; we see it as a 0-length CSW message. The real CSW follows
immediately after. (Or sometimes a STALL follows immediately after, with
the real CSW coming after that!)
The patch checks the results of the first attempt to read the CSW. If it
sees a normal packet (not a STALL) with length 0, it retries the read.
Reports from two users indicate that it improves the performance of their
USB-2 DVD drives.
drivers/usb/storage/transport.c | 13 ++++++++++++-
1 files changed, 12 insertions(+), 1 deletion(-)
diff -Nru a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
--- a/drivers/usb/storage/transport.c Thu Feb 19 17:22:17 2004
+++ b/drivers/usb/storage/transport.c Thu Feb 19 17:22:17 2004
@@ -929,6 +929,7 @@
unsigned int residue;
int result;
int fake_sense = 0;
+ unsigned int cswlen;
/* set up the command wrapper */
bcb->Signature = cpu_to_le32(US_BULK_CB_SIGN);
@@ -985,7 +986,17 @@
/* get CSW for device status */
US_DEBUGP("Attempting to get CSW...\n");
result = usb_stor_bulk_transfer_buf(us, us->recv_bulk_pipe,
- bcs, US_BULK_CS_WRAP_LEN, NULL);
+ bcs, US_BULK_CS_WRAP_LEN, &cswlen);
+
+ /* Some broken devices add unnecessary zero-length packets to the
+ * end of their data transfers. Such packets show up as 0-length
+ * CSWs. If we encounter such a thing, try to read the CSW again.
+ */
+ if (result == USB_STOR_XFER_SHORT && cswlen == 0) {
+ US_DEBUGP("Received 0-length CSW; retrying...\n");
+ result = usb_stor_bulk_transfer_buf(us, us->recv_bulk_pipe,
+ bcs, US_BULK_CS_WRAP_LEN, &cswlen);
+ }
/* did the attempt to read the CSW fail? */
if (result == USB_STOR_XFER_STALLED) {
-------------------------------------------------------
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