netdev - Re: [PATCH v1 1/4] USB: introduce usb_device_no_sg

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Message-ID: <CACVXFVMNEeF2cLqvqciKdDO8W_UdSbQ2UC5grpDenmQrX-5=XQ@mail.gmail.com>
Date:	Sun, 4 Aug 2013 08:22:18 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Oliver Neukum <oneukum@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v1 1/4] USB: introduce usb_device_no_sg_limit() helper

On Sat, Aug 3, 2013 at 11:53 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Sat, 3 Aug 2013, Ming Lei wrote:
>
>> 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.
>
>> 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
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