Hi,
> The problem needs to be fixed one way or another. It sounds like Ravi
> wants to move the solution upstream ("I think we need to fix the root
> cause by ensuring that ownership bit is cleared before the bd is reclaimed
> and added to the freelist." - Ravi) from where I tackled it, which makes
> good sense.
Can you now look into the issue and find the root cause, once completed
Please resubmit the updated patch.
Ravi B
>
> Thanks,
> Paul
>
> -----Original Message-----
> From: Felipe Balbi [mailto:balbi@xxxxxx]
> Sent: Friday, January 07, 2011 1:43 AM
> To: B, Ravi
> Cc: Paul Stuart; linux-usb@xxxxxxxxxxxxxxx; Davinci-linux-open-
> source@xxxxxxxxxxxxxxxxxxxx; sshtylyov@xxxxxxxxxx; Balbi, Felipe; Nori,
> Sekhar
> Subject: Re: [PATCH v2] USB: musb: Prevent Transmit Buffer Descriptor
> corruption
>
> On Mon, Jan 03, 2011 at 07:07:06PM +0530, B, Ravi wrote:
> > Hi,
> > > cppi_next_tx_segment is not checking for Transmit Buffer Descriptor
> > > ownership before modifying parameters.
> > >
> > > Transmit Buffer Descriptor ram is shared between the host processor
> and
> > > the DMA. The "Ownership" bit is set by the host processor to give the
> > > DMA ownership of the Transmit Buffer Descriptor, and the bit is
> cleared
> > > by the DMA to return ownership to the host processor.
> > >
> > > On USB Tx, when the system is heavily loaded, cppi_next_tx_segment can
> > > overwrite a Transmit Buffer Descriptor that is still owned by the DMA,
> > > causing DMA truncation error to fire, resulting in a channel abort.
> This
> > > proposed fix adds a check for host processor ownership of the bd and
> > > does not proceed to program it until the DMA has ended ownership.
> > [...]
> > > --- a/drivers/usb/musb/cppi_dma.c 2010-12-06 20:09:04.000000000 -
> 0800
> > > +++ b/drivers/usb/musb/cppi_dma.c 2010-12-07 11:22:04.000000000 -
> 0800
> > > @@ -625,6 +625,14 @@ cppi_next_tx_segment(struct musb *musb,
> > > * size; for RNDIS there _is_ only that last packet.
> > > */
> > > for (i = 0; i < n_bds; ) {
> > > +
> > > + /* wait for DMA to release ownership of this bd */
> > > + if (unlikely(bd->hw_options & CPPI_OWN_SET)) {
> > > + do {
> > > + cpu_relax();
> > > + } while (bd->hw_options & CPPI_OWN_SET);
> > > + }
> > > +
> > The bd has been taken from freelist and therefore should have ownership
> > Bit already cleared. I think we need to fix the root cause by ensuring
> > that ownership bit is cleared before the bd is reclaimed and added to
> > the freelist.
>
> ping... do we need this patch ?
>
> --
> balbi
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