linux-kernel - RE: [PATCH V2 2/2] usb: musb: Stop bulk endpoint while queue is rotated

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Message-ID: <6b25b4a5cc104ea0adc5bd006040529b@SEHSTE15D2BE2.hs20.net>
Date:	Mon, 23 May 2016 13:26:22 +0000
From:	Andrew Goodbody <andrew.goodbody@...brionix.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	"b-liu@...com" <b-liu@...com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH V2 2/2] usb: musb: Stop bulk endpoint while queue is
 rotated

> From: Sergei Shtylyov [mailto:sergei.shtylyov@...entembedded.com]
> 
> Hello.
> 
> On 5/23/2016 3:00 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@...brionix.com>
> > Cc: stable@...r.kernel.org
> > ---
> > 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.

> > +		 * 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? I do not understand what you mean by the "abstract" manual. Would you be OK with "ref MUSB Programmer's Guide section 9.2.2"

Andrew

> [...]
> 
> MBR, Sergei