Re: [PATCH V2 2/2] usb: musb: Stop bulk endpoint while queue is rotated

[Sergei Shtylyov]

On 5/23/2016 4:26 PM, Andrew Goodbody wrote:

> > > Ensure that the endpoint is stopped by clearing REQPKT before clearing
> > > DATAERR_NAKTIMEOUT before rotating the queue on the dedicated bulk
> > > endpoint.
> > > This addresses an issue where a race could result in the endpoint
> > > receiving data before it was reprogrammed resulting in a warning about
> > > such data from musb_rx_reinit before it was thrown away.
> > > The data thrown away was a valid packet that had been correctly ACKed
> > > which meant the host and device got out of sync.
> > >
> > > Signed-off-by: Andrew Goodbody <andrew.goodbody@xxxxxxxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > ---
> > > V2 added comment about clearing REQPKT before DATAERR_NAKTIMEOUT
> > >
> > >  drivers/usb/musb/musb_host.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/drivers/usb/musb/musb_host.c
> > > b/drivers/usb/musb/musb_host.c index 2966596..676cb98 100644
> > > --- a/drivers/usb/musb/musb_host.c
> > > +++ b/drivers/usb/musb/musb_host.c
> > > @@ -997,6 +997,12 @@ static void musb_bulk_nak_timeout(struct musb
> > *musb, struct musb_hw_ep *ep,
> > >  		/* clear nak timeout bit */
> > >  		rx_csr = musb_readw(epio, MUSB_RXCSR);
> > >  		rx_csr |= MUSB_RXCSR_H_WZC_BITS;
> > > +		/*
> > > +		 * Need to stop the transaction by clearing REQPKT before
> >
> >     Transcation? Maybe transfer?
>
> The quote from the TRM is "If the DATAERR_NAKTIMEOUT bit is set, the controller can be directed either to continue trying this transaction (until it times out again) by clearing the DATAERR_NAKTIMEOUT bit or to abort the transaction by clearing REQPKT bit before clearing the DATAERR_NAKTIMEOUT bit."
> So 'transaction' is correct.

   OK.

> > > +		 * DATAERR_NAKTIMEOUT ref TRM section 16.3.8.2.2.1.2
> >
> >     Which TRM? Do you understand that the MUSB core is used by multiple
> > SoCs?
> > I'd recommend referring just to the "abstract" manual or the MUSB
> > programmer's guide (section 9.2.2 if you want an exact ref.).

> That would be the AM335x Sitara Processors TRM. I don't have the MUSB programmer's guide, is it available online somewhere?

   AFAIK, no.

> I do not understand what you mean by the "abstract" manual.

   Just saying "the manual" or "the manuals".

> Would you be OK with "ref MUSB Programmer's Guide section 9.2.2"

   Yes. However, that spec calls the bit just "NAK Timeout" in this context, 
not DATAERR_NAKTIMEOUT. Overall, this spec. uses CamelCase for the register 
bit names (I recall dbrownell complaining over that and uppercase all the bit 
names in my patches :-).

> Andrew
>
> > [...]

MBR, Sergei