[U-Boot] [PATCH] usb: xhci: Limit transfer length in a single TD

[Dongwoo Lee]

The transfer request exceeding 4032KB (the maximum number of TRBs per
TD * the maximum size of transfer buffer on TRB) fails on xhci host
with timed out error or babble error state. This failure occurs when
accessing large files on USB mass-storage. Currently with xhci as well
as ehci host, the driver requests maximum 30MB (65536 blks * 512 byte)
to storage at once. However, xhci cannot handle this request because
of the reason mentioned above, even though ehci can handle this. Thus,
transfer request larger than this size should be splitted in order to
limit the length of data in a single TD.

Even though the single request is splitted into multiple requests,
the transfer speed has affected insignificantly in comparison with
ehci host: 22.6 MB/s on ehci and 22.3 MB/s on xhci for 100MB tranfer.

Reported-by: Jaehoon Chung <jh80.chung at samsung.com>
Signed-off-by: Dongwoo Lee <dwoo08.lee at samsung.com>
---
 drivers/usb/host/xhci.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 3201177..594026e 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -907,12 +907,40 @@ static int _xhci_submit_int_msg(struct usb_device *udev, unsigned long pipe,
 static int _xhci_submit_bulk_msg(struct usb_device *udev, unsigned long pipe,
 				 void *buffer, int length)
 {
+	int ret;
+	int xfer_max_per_td, xfer_length, buf_pos;
+
 	if (usb_pipetype(pipe) != PIPE_BULK) {
 		printf("non-bulk pipe (type=%lu)", usb_pipetype(pipe));
 		return -EINVAL;
 	}
 
-	return xhci_bulk_tx(udev, pipe, length, buffer);
+	/*
+	 * When transfering data exceeding the maximum number of TRBs per
+	 * TD (default 64) is requested, the transfer fails with babble
+	 * error or time out.
+	 *
+	 * Thus, huge data transfer should be splitted into multiple TDs.
+	 */
+	xfer_max_per_td = TRB_MAX_BUFF_SIZE * (TRBS_PER_SEGMENT - 1);
+
+	buf_pos = 0;
+	do {
+		if (length > xfer_max_per_td)
+			xfer_length = xfer_max_per_td;
+		else
+			xfer_length = length;
+
+		ret = xhci_bulk_tx(udev, pipe, xfer_length, buffer + buf_pos);
+		if (ret < 0)
+			return ret;
+
+		buf_pos += xfer_length;
+		length -= xfer_length;
+
+	} while (length > 0);
+
+	return ret;
 }
 
 /**
-- 
1.9.1