# RE: \[RFC\] \[PATCH\] usb: gadget: fix dtd dma confusion

- From: Chen Peter-B29397 \<hidden\>
- Date: 2012-05-14 01:11:17 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2012/05/9469367
- Thread: https://ratatoskr.run/linuxppc-dev/2012/05/9469338/t.md

```text
=20


=20
> > See here:
> > daec765da767e4a6a30e1298862b28f2cae9a73f
> > usb: gadget: mv_udc: fix dtd dma confusion
> >
> > So hereby I'm CC-ing all *udc.c maintainers to point out that this
> > issue maybe affects you too.
> >
> >
> > ---
> > Subject: [PATCH] usb: gadget: fsl_udc: fix dtd dma confusion
> >
> > The controller will hang when doing testings with g_ether and iperf
> > (tool for measuring maximum TCP and UDP bandwidth).  This patch adds a
> > delay to wait for controller to release dtd dma before freeing it.
> >
> > Signed-off-by: Christoph Fritz <redacted>
> > ---
> >  drivers/usb/gadget/fsl_udc_core.c |    9 +++++++++
> >  1 files changed, 9 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/fsl_udc_core.c
> b/drivers/usb/gadget/fsl_udc_core.c
> > index 55abfb6..fc86108 100644
> > --- a/drivers/usb/gadget/fsl_udc_core.c
> > +++ b/drivers/usb/gadget/fsl_udc_core.c
> > @@ -1638,6 +1638,15 @@ static int process_ep_req(struct fsl_udc *udc,
> int pipe,
> >  			status =3D REQ_UNCOMPLETE;
> >  			return status;
> >  		} else if (remaining_length) {
> > +			/* wait controller release dtd dma */
> > +			while ((curr_qh->curr_dtd_ptr =3D=3D curr_td->td_dma)) {
> > +				if (curr_td->next_td_ptr =3D=3D
> > +						EP_QUEUE_HEAD_NEXT_TERMINATE) {
> > +					udelay(100);
> > +					break;
> > +				}
> > +				udelay(1);
> > +			}
> >  			if (direction) {
> >  				VDBG("Transmit dTD remaining length not zero");
> >  				status =3D -EPROTO;
> > --
> > 1.7.2.5
>=20
>  ping  -  what about this patch? Will it be applied?
>=20
Christoph, it is better use errata suggests workaround (postpone free dtd m=
emory),
and you can find related code at:=20

http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/tree/
drivers/usb/gadget/arcotg_udc.c?h=3Dimx_3.0.15

The code is defined with POSTPONE_FREE_LAST_DTD

> Thanks,
>  -- Christoph
>=20
```