RE: [PATCH 5/5] usb: dwc3: fix DMA offset calculation

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> From: Felipe Balbi [mailto:balbi@xxxxxx]
> Sent: Wednesday, September 28, 2011 3:30 AM
> 
> Hi,
> 
> On Tue, Sep 27, 2011 at 10:53:32PM -0700, Paul Zimmerman wrote:
> > Fix offset calculation in dwc3_trb_dma_offset()
> >
> > Signed-off-by: Paul Zimmerman <paulz@xxxxxxxxxxxx>
> > ---
> >  drivers/usb/dwc3/gadget.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index 5283956..2c68934 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -189,7 +189,7 @@ int dwc3_send_gadget_ep_cmd(struct dwc3 *dwc, unsigned ep,
> >  static dma_addr_t dwc3_trb_dma_offset(struct dwc3_ep *dep,
> >  		struct dwc3_trb_hw *trb)
> >  {
> > -	u32		offset = trb - dep->trb_pool;
> > +	u32	offset = (char *)trb - (char *)dep->trb_pool;
> 
> Have you really seen anything wrong with this ? Also, I'm not sure a
> char would be good here. Maybe unsigned long would be better. Also,
> don't change the alignment :-)

Yes, I definitely saw something wrong with this. The DMA address for the
first TRB was <address>, and for the second TRB it was <address> + 1,
where it should have been <address> + 16. For some reason it only showed
up after a disconnect/reconnect cycle, but it was definitely wrong.

Not sure what you mean about unsigned long and alignment. This is pretty
basic pointer math, I think the way I did it is the correct fix. The other
alternative would be (trb - dep->trb_pool) * sizeof(struct dwc3_trb_hw),
but I like mine better.

-- 
Paul

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