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

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Date:	Thu, 27 Feb 2014 01:12:10 -0800
From:	Neil Zhang <zhangwm@...vell.com>
To:	"balbi@...com" <balbi@...com>
CC:	Peter Chen <Peter.Chen@...escale.com>,
	"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 23:19
> To: Neil Zhang
> Cc: balbi@...com; Peter Chen; 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 05:48:17PM -0800, Neil Zhang 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.
> 
> that's nonsense, the average chipidea glue layer is ~80 LOCs. You can write
> that in less than 2 hours and give it a try. We cannot have duplicate drivers in
> the tree and development effort *must* be shared.
> 
> If you guys use the same IP, why wouldn't you use the same chipidea driver ?
> 
> sorry, you didn't convince me.

It's too sad!
Anyway we will estimate the chipidea driver to see whether it meets our requirement.

> 
> --
> Balbi

Best Regards,
Neil Zhang