[RFC] [PATCH] usb: gadget: fix dtd dma confusion

[Neil Zhang]

> -----Original Message-----
> From: Christoph Fritz [mailto:chf.fritz at googlemail.com]
> Sent: 2012年5月9日 13:38
> To: Chen Peter-B29397; Chao Xie
> Cc: Neil Zhang; Fabio Estevam; Li Yang-R58472; Felipe Balbi; Greg
> Kroah-Hartman; linux-usb at vger.kernel.org; linuxppc-dev at lists.ozlabs.org;
> Hans J. Koch; Daniel Mack; Thomas Dahlmann; Nicolas Ferre; Eric Miao;
> Russell King; Haojian Zhuang; Ben Dooks; Kukjin Kim; Sascha Hauer;
> Oliver Neukum; Ido Shayevitz; Estevam Fabio-R49496
> Subject: Re: [RFC] [PATCH] usb: gadget: fix dtd dma confusion
> 
> Hi Peter,
> 
>  thanks you for your help.
> 
> On Wed, May 09, 2012 at 02:11:56AM +0000, Chen Peter-B29397 wrote:
> >
> >
> > > >
> > > > after a while of testing and searching I can come up with a patch
> > > > that fixes g_ether <-> iperf for fsl_udc on ARM i.MX35.
> > > >
> > > > The sad part is that this kind of fix is already implemented for
> > > > marvell mv_udc driver since last year but still _not_ in the ~15
> > > > other *udc.c drivers.
> > > >
> >
> > It is a controller limitation (bug?) for chipidea controller when
> using
> > dtd list to handle multi-dtds situation. The controller will read
> dtd's
> > next pointer after this dtd's active bit has already been cleared.
> >
> > Freescale has an errata for this problem's description and solution.
> > http://cache.freescale.com/files/dsp/doc/errata/IMX23CE.pdf
> > See 2858
> 
> I'm hacking here an i.MX35 not an i.MX23. So I already had a look at
> its
> errata sheet
> http://cache.freescale.com/files/dsp/doc/errata/IMX35CE.pdf
> but didn't find a similar "limitation" as you now pointed out by errata
> number 2858 for i.MX23.
> 
> What about the fix for mv_udc, shouldn't they have a similar
> "limitation"? How do you explain?
> Or maybe someone from Marvell has an answer?
> 

Yes, we encountered the same issue, and I have answered your question several hours ago.
Please have a look.

> 
> Thanks,
>  -- Christoph

Best Regards,
Neil Zhang