From: Felipe Balbi <balbi@ti.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Felipe Balbi <balbi@ti.com>,
sundeep subbaraya <sundeep.lkml@gmail.com>,
Subbaraya Sundeep Bhatta <subbaraya.sundeep.bhatta@xilinx.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Michal Simek <michals@xilinx.com>,
Subbaraya Sundeep Bhatta <sbhatta@xilinx.com>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH RFC] usb: gadget: Add xilinx axi usb2 device support
Date: Tue, 15 Apr 2014 23:39:23 -0500 [thread overview]
Message-ID: <20140416043922.GC15056@saruman.home> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1404151345580.1310-100000@iolanthe.rowland.org>
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Hi,
On Tue, Apr 15, 2014 at 01:55:38PM -0400, Alan Stern wrote:
> On Tue, 15 Apr 2014, Felipe Balbi wrote:
>
> > > 2. Does device need to know OUT transactions before hand so that OUT
> > > requests are queued for endpoint before packets are received
> > > from host?
> >
> > well, no. Gadget driver shouldn't depend on that. That's UDC driver's
> > responsability to manage that. I mean, if host sends OUT token and
> > there's nothing in the out queue, then UDC need to start transfer as
> > soon as gadget driver queues the request. If, on the other hand, gadget
> > driver queues packet before host has sent OUT token then you have two
> > choices:
> >
> > 1) start the transfer - most HW will wait for OUT token
> > 2) wait for out token
>
> I'm not familiar with the variations in all the different UDC hardware.
> Nevertheless, I wouldn't describe the situation in those terms.
OK, I've oversimplified... what I meant was that even if you start a
transfer at the UDC level, nothing will happen on the bus until HW sees
an OUT token. The buffer pointed to by req->buf won't get any writes,
DMA won't do anything.
On (2) I meant that some HW (e.g. dwc3) will assert the IRQ line once
they see a token for which they have to transfer descriptors in the
internal controller's cache.
> If an OUT transaction occurs and the gadget driver hasn't queued a
> request, the UDC hardware could store the incoming data in an internal
> buffer or it could NAK the transaction. There aren't any other
> choices. If there isn't enough space available in an internal buffer,
> the only possible action is NAK.
in HS there's also NYET
> Regardless, gadget drivers do not need to queue requests for OUT
> endpoints before the host starts sending data. When the request does
they're not required, but they can. It's UDC driver's responsability to
start consuming the queue at the proper time.
> get queued, the UDC driver will make sure that the transfer takes
> place.
correct.
--
balbi
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prev parent reply other threads:[~2014-04-16 4:41 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-19 9:40 [PATCH RFC] usb: gadget: Add xilinx axi usb2 device support Subbaraya Sundeep Bhatta
2014-02-20 18:23 ` Felipe Balbi
2014-02-21 6:38 ` Michal Simek
2014-02-21 16:04 ` Greg Kroah-Hartman
2014-02-21 16:04 ` Michal Simek
2014-02-21 16:12 ` SPDX-License-Identifier (was: Re: [PATCH RFC] usb: gadget: Add xilinx axi usb2 device support) Felipe Balbi
2014-02-21 16:18 ` SPDX-License-Identifier Michal Simek
2014-02-21 16:20 ` SPDX-License-Identifier Felipe Balbi
2014-02-21 16:56 ` SPDX-License-Identifier Greg Kroah-Hartman
2014-02-21 17:26 ` SPDX-License-Identifier Michal Simek
2014-02-21 17:57 ` SPDX-License-Identifier Greg Kroah-Hartman
2014-02-21 19:01 ` SPDX-License-Identifier Theodore Ts'o
2014-02-24 10:12 ` SPDX-License-Identifier Michal Simek
2014-02-24 13:41 ` SPDX-License-Identifier Theodore Ts'o
2014-02-24 14:03 ` SPDX-License-Identifier Michal Simek
2014-02-24 14:26 ` SPDX-License-Identifier Greg Kroah-Hartman
2014-02-25 12:10 ` SPDX-License-Identifier One Thousand Gnomes
2014-02-25 12:25 ` SPDX-License-Identifier Geert Uytterhoeven
2015-02-02 15:43 ` SPDX-License-Identifier Stefan Roese
2015-02-02 16:06 ` SPDX-License-Identifier Greg Kroah-Hartman
2015-02-04 16:41 ` SPDX-License-Identifier Stefan Roese
2015-02-05 4:21 ` SPDX-License-Identifier Theodore Ts'o
2015-02-05 6:41 ` SPDX-License-Identifier Greg Kroah-Hartman
2015-02-25 21:49 ` SPDX-License-Identifier Pavel Machek
2015-02-25 22:00 ` SPDX-License-Identifier Felipe Balbi
2015-02-26 21:49 ` SPDX-License-Identifier Pavel Machek
2015-02-26 10:26 ` SPDX-License-Identifier One Thousand Gnomes
2015-02-26 13:39 ` SPDX-License-Identifier Theodore Ts'o
2015-02-26 21:53 ` SPDX-License-Identifier Pavel Machek
2015-02-05 11:49 ` SPDX-License-Identifier One Thousand Gnomes
2014-02-21 16:23 ` [PATCH RFC] usb: gadget: Add xilinx axi usb2 device support Greg Kroah-Hartman
2014-02-21 11:27 ` Subbaraya Sundeep Bhatta
2014-02-21 15:39 ` Felipe Balbi
2014-03-10 13:36 ` sundeep subbaraya
2014-03-10 18:44 ` Felipe Balbi
2014-02-21 12:04 ` Mark Rutland
2014-02-21 13:41 ` Michal Simek
2014-02-21 13:57 ` Mark Rutland
2014-02-21 14:06 ` Michal Simek
2014-02-21 15:42 ` Felipe Balbi
2014-02-21 15:51 ` Michal Simek
2014-02-21 16:00 ` Felipe Balbi
2014-02-21 16:15 ` Arnd Bergmann
2014-02-21 15:41 ` Felipe Balbi
2014-02-21 16:13 ` Mark Rutland
2014-03-26 10:07 ` sundeep subbaraya
2014-04-15 17:18 ` Felipe Balbi
2014-04-15 17:55 ` Alan Stern
2014-04-16 4:39 ` Felipe Balbi [this message]
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