linux-kernel - Re: [PATCH] usb: core: allow zero packet flag for interrupt urbs

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Date:	Mon, 21 Jul 2014 10:37:37 +0530
From:	Amit Virdi <amit.virdi@...com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"rdunlap@...radead.org" <rdunlap@...radead.org>,
	"ming.lei@...onical.com" <ming.lei@...onical.com>,
	"hdegoede@...hat.com" <hdegoede@...hat.com>
Subject: Re: [PATCH] usb: core: allow zero packet flag for interrupt urbs

On 7/18/2014 8:09 PM, Alan Stern wrote:
> On Fri, 18 Jul 2014, Amit Virdi wrote:
>
>> On 7/17/2014 8:25 PM, Alan Stern wrote:
>>> I can't say this is actually wrong, but have you ever encountered a
>>> situation where this would be needed?  How often does anyone need to do
>>> a multi-packet transfer over an interrupt endpoint?
>>
>> Honestly, I haven't found any such real device yet. I did this change
>> while I was going through the code when adding support for interrupt
>> transfers in gadget zero. I'm a no expert, but the spec says it should
>> be supported so this code should be added.
>
> I just remembered, the HID spec requires that all reports (except the
> longest) end with a short packet.  And since output reports are allowed
> to be sent over an Interrupt-OUT endpoint, we have to accept the
> URB_ZERO_PACKET flag for interrupt URBs.
>

Ok, great!

>> However, I messed up a little in this patch. It should have been
>> ---
>>           case USB_ENDPOINT_XFER_ISOC:
>>                   allowed |= URB_ISO_ASAP;
>>                   break;
>> +       case USB_ENDPOINT_XFER_INT:
>> +               if (is_out)
>> +                       allowed |= URB_ZERO_PACKET;
>> +               else
>> +                       allowed |= URB_SHORT_NOT_OK;
>> +               break;
>>           }
>>           allowed &= urb->transfer_flags;
>>
>> ---
>> Otherwise, it sets zero packet flag for control out transfers too.
>>
>> I'll send a V2 with this change if you agree to setting of the zero
>> packet flag for interrupt transfers.
>
> How about this change instead?
>
>   			URB_FREE_BUFFER);
>   	switch (xfertype) {
>   	case USB_ENDPOINT_XFER_BULK:
> +	case USB_ENDPOINT_XFER_INT:

Looks better.
I'll submit a V2 with this change.

Regards
Amit Virdi
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