linux-kernel - Re: [PATCHv3 3/4] usb: gadget: rename usb_gadget_driver::speed to max

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Date:	Mon, 22 Aug 2011 13:42:21 +0300
From:	Felipe Balbi <balbi@...com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Felipe Balbi <balbi@...com>,
	Michal Nazarewicz <mnazarewicz@...gle.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Yang Rui Rui <ruirui.r.yang@...to.com>,
	Dave Young <hidave.darkstar@...il.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 3/4] usb: gadget: rename usb_gadget_driver::speed to
 max_speed

Hi,

On Fri, Aug 19, 2011 at 10:34:29PM -0400, Alan Stern wrote:
> On Sat, 20 Aug 2011, Felipe Balbi wrote:
> 
> > On Sat, Aug 20, 2011 at 12:33:01AM +0200, Michal Nazarewicz wrote:
> > > From: Michal Nazarewicz <mina86@...a86.com>
> > > 
> > > This commit renames the “speed”	field of the usb_gadget_driver
> > > structure to “max_speed”.  This is so that to make it more
> > > apparent that the field represents the maximum speed gadget
> > > driver can support.
> > > 
> > > This also make the field look more like fields with the same
> > > name in usb_gadget and usb_composite_driver structures.  All
> > > of those represent the *maximal* speed given entity supports.
> > > 
> > > After this commit, there are the following fields in various
> > > structures:
> > > * usb_gadget::speed - the current connection speed,
> > > * usb_gadget::max_speed - maximal speed UDC supports,
> > 
> > this will be handled inside the UDC itself, so why do you need to expose
> > it ?
> 
> I wondered about this too.  It turns out that sometimes the gadget
> driver really does need to know about the maximum speed supported by
> the UDC hardware and driver.
> 
> For example, suppose the gadget driver and the UDC both support high
> speed, but the gadget is currently plugged into a USB-1.1 controller
> and therefore running only at full speed.  Then the gadget driver has
> to respond to the Get-Device-Qualifier and Get-Other-Speed-Config
> requests by sending the appropriate descriptors.  But if the UDC
> doesn't support high speed operation then the gadget driver has to
> respond to those requests with a STALL.

aa, good point :-)

-- 
balbi

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