xhci: dbc: Improve performance by removing delay in transfer event polling.

Queue event polling work with 0 delay in case there are pending transfers
queued up. This is part 2 of a 3 part series that roughly triples dbc
performace when using adb push and pull over dbc.

Max/min push rate after patches is 210/118 MB/s, pull rate 171/133 MB/s,
tested with large files (300MB-9GB) by Łukasz Bartosik

First performance improvement patch was commit 31128e7
("xhci: dbc: add dbgtty request to end of list once it completes")

Cc: Łukasz Bartosik <[email protected]>
Signed-off-by: Mathias Nyman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: matnyman

drivers/usb/host/xhci-dbgcap.c

@@ -957,7 +957,7 @@ static void xhci_dbc_handle_events(struct work_struct *work)
 		/* set fast poll rate if there are pending data transfers */
 		if (!list_empty(&dbc->eps[BULK_OUT].list_pending) ||
 		    !list_empty(&dbc->eps[BULK_IN].list_pending))
-			poll_interval = 1;
+			poll_interval = 0;
 		break;
 	default:
 		dev_info(dbc->dev, "stop handling dbc events\n");