linux-kernel - Re: [PATCH v2 2/2] usb: gadget: Add xilinx axi usb2 device support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Pine.LNX.4.44L0.1404220956210.1326-100000@iolanthe.rowland.org>
Date:	Tue, 22 Apr 2014 09:57:26 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	sundeep subbaraya <sundeep.lkml@...il.com>
cc:	Felipe Balbi <balbi@...com>,
	Subbaraya Sundeep Bhatta <subbaraya.sundeep.bhatta@...inx.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Michal Simek <michals@...inx.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Subbaraya Sundeep Bhatta <sbhatta@...inx.com>
Subject: Re: [PATCH v2 2/2] usb: gadget: Add xilinx axi usb2 device support

On Tue, 22 Apr 2014, sundeep subbaraya wrote:

> Hi,
> 
> On Mon, Apr 21, 2014 at 10:09 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Mon, 21 Apr 2014, Felipe Balbi wrote:
> >
> >> Hi,
> >>
> >> On Fri, Apr 18, 2014 at 07:34:08PM +0530, sundeep subbaraya wrote:
> >>
> >> <snip>
> >>
> >> > >> in ep_queue driver starts dma transfer from/to IP buffer to/from req->buf.
> >> > >> If transfer is completed then request is not added to ep request queue
> >> > >> and returns from ep_queue.
> >> > >> If transfer is not completed (actual < length) then request is added
> >> > >> to queue and returns from ep_queue.
> >> > >
> >> > > This is wrong. Why wouldn't you give gadget driver the chance to decide
> >> > > if it needs to queue the request again or not ?
> >> >
> >> > When does gadget driver decides to queue the same request again?
> >> > if -EBUSY is returned from ep_queue or req.status != 0 in completion
> >> > routine?
> >>
> >> whenever it so decides. Different gadget drivers might have different
> >> requirements. The code is open and sits under drivers/usb/gadget/ why
> >> don't you have a read ?
> >
> > I get the impression that the two of you are arguing past each other.
> > It appears that Sundeep is talking about transferring data from the
> > gadget driver's buffer to an internal buffer in the UDC hardware, but
> > Felipe is talking about transferring data from the UDC to the host.
> >
> > As I understand it, Sundeep said that when the gadget driver queues a
> > data-IN request, the UDC driver copies as much of the data buffer as
> > possible into a hardware FIFO.  If it succeeds in copying all the data
> > into the FIFO then the request's completion routine gets called
> > immediately, even though the data doesn't get sent from the FIFO to the
> > host until the host asks for it.
> >
> > If only part of the data can be copied into the FIFO then the request
> > is added to the ep's request queue before the usb_ep_queue() call
> > returns.  When space becomes available in the FIFO, the data will be
> > copied and eventually sent to the host.  When all the data has been
> > copied to the FIFO, the request's completion routine will be called.
> >
> > Thus there never is any need for the gadget driver to queue the request
> > again.  An incomplete transfer means the FIFO didn't have enough room
> > when the request was submitted; it doesn't mean that the data didn't
> > eventually get sent to the host.
> 
> Exactly Alan,this is what I was trying to say. Probably I was not
> clear in explaining. I didnt see
> any harm this way and even this implementation is same like
> at91_udc.c. I have been reading
> mas_storage to understand when does gadget driver tries to enqueue a
> request again. Since
> different gadget drivers might have different requirements (agree with
> Felipe), wanted to
> know criteria for queuing a same request again.
> 
> I will change this implementation as per Felipe comments and test with
> some of the gadgets.

Wait until you hear what Felipe has to say about this discussion.  
Maybe he will decide that the original implementation was correct.

Alan Stern

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/