linux-kernel - RE: [PATCH 2/6] usb: gadget: mv

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Date:	Tue, 25 Feb 2014 17:48:17 -0800
From:	Neil Zhang <zhangwm@...vell.com>
To:	"balbi@...com" <balbi@...com>,
	Peter Chen <Peter.Chen@...escale.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: RE: [PATCH 2/6] usb: gadget: mv_udc: disable HW zlt for ep0


> -----Original Message-----
> From: Felipe Balbi [mailto:balbi@...com]
> Sent: 2014年2月26日 2:13
> To: Peter Chen
> Cc: Neil Zhang; balbi@...com; gregkh@...uxfoundation.org;
> linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org; Alexander Shishkin
> Subject: Re: [PATCH 2/6] usb: gadget: mv_udc: disable HW zlt for ep0
> 
> Hi,
> 
> On Tue, Feb 25, 2014 at 07:46:08AM +0000, Peter Chen wrote:
> > > > > > > Hardware zlt will try to send the zero length packet
> > > > > > > automatically when the data transferd is multiple times of
> > > > > > > max packet, this will cause issues on Windows.
> > > > > > > So let's disable HW zlt by default.
> > > > > >
> > > > > > Would you have description that what kinds of issue on Windows
> > > > > > if zlt is is selected?
> > > > > >
> > > > >
> > > > > Enumeration will fail.
> > > > >
> > > >
> > > > What causes enumeration fail, why it does not occur before?
> > > >
> > > A unexpected zero packet cause enumeration fail.
> > > It's not easy that the descriptor is actually 1024 bytes, so not
> > > easy to be found.
> > >
> >
> > Chipidea bug too? Does it follow ch 8.5.3.2 Variable-length Data Stage, USB
> 2.0 spec?
> 
> wait, this is a chipidea core ? Why aren't you guys using the chipidea driver
> yet ? You need to switch over to that driver dude, we can't have duplicated
> code in the tree.
> 
> I'm sorry, but I won't be taking this series, please use chipidea driver, it should
> be very simple to add a glue layer for your core to the chipidea driver.
> 

Yes, it use chipidea IP.
But the driver is earlier than the chipidea one and we use it for our products.
So it may be not that easy to switch to chipidea driver due to the stability.

> --
> Balbi

Best Regards,
Neil Zhang