[PATCH 01/12] xhci: If no endpoints changed, don't issue BW command.

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Some alternate interface settings have no endpoints associated with them.
This shows up in some USB webcams, particularly the Logitech HD 1080p,
which uses the uvcvideo driver.  If a driver switches between two alt
settings with no endpoints, there is no need to issue a configure endpoint
command, because there is no endpoint information to update.

The only time a configure endpoint command with just the add slot flag set
makes sense is when the driver is updating hub characteristics in the slot
context.  However, that code never calls xhci_check_bandwidth, so we
should be safe not issuing a command if only the slot context add flag is
set.

Signed-off-by: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>
---
 drivers/usb/host/xhci.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index f647d91..fcc5821 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -1888,6 +1888,12 @@ int xhci_check_bandwidth(struct usb_hcd *hcd, struct usb_device *udev)
 	ctrl_ctx->add_flags |= cpu_to_le32(SLOT_FLAG);
 	ctrl_ctx->add_flags &= cpu_to_le32(~EP0_FLAG);
 	ctrl_ctx->drop_flags &= cpu_to_le32(~(SLOT_FLAG | EP0_FLAG));
+
+	/* Don't issue the command if there's no endpoints to update. */
+	if (ctrl_ctx->add_flags == cpu_to_le32(SLOT_FLAG) &&
+			ctrl_ctx->drop_flags == 0)
+		return 0;
+
 	xhci_dbg(xhci, "New Input Control Context:\n");
 	slot_ctx = xhci_get_slot_ctx(xhci, virt_dev->in_ctx);
 	xhci_dbg_ctx(xhci, virt_dev->in_ctx,
-- 
1.7.4.1

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