Re: [PATCH v1 1/4] USB: introduce usb_device_no_sg_limit() helper

On Sat, Aug 3, 2013 at 11:53 PM, Alan Stern [off-list ref] wrote:

On Sat, 3 Aug 2013, Ming Lei wrote:

quoted

Some host controllers(such as xHCI) can support building
packet from discontinuous buffers, so introduce one flag
and helper for this kind of host controllers, then the
feature can help some applications(such as, usbnet) by
supporting arbitrary length of sg buffers.

quoted

diff --git a/include/linux/usb.h b/include/linux/usb.h
index 84f14e2..5d03074 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h

@@ -337,6 +337,7 @@ struct usb_bus {
                                       * the ep queue on a short transfer
                                       * with the URB_SHORT_NOT_OK flag set.
                                       */
+     unsigned no_sg_limit:1;         /* no sg list limit */

Why do you call this "no_sg_limit"?  It isn't a limit on the SG list;
the list can be arbitrarily long, provided all the entries except the
last are divisible by the maxpacket size.

You could call it "no_sg_constraint" if you want.  Or
"allow_arbitrary_sg", to put a more positive spin on it.

OK, I prefer no_sg_constraint, and will do it in v2.

Thanks,
--
Ming Lei