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

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Date:	Fri, 20 May 2016 20:14:09 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Andrew Goodbody <andrew.goodbody@...brionix.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 2/2] usb: musb: Stop bulk endpoint while queue is rotated

On 05/20/2016 08:06 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
>>> ---
>>>  drivers/usb/musb/musb_host.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/usb/musb/musb_host.c
>>> b/drivers/usb/musb/musb_host.c index 30e0d65..777ff30 100644
>>> --- a/drivers/usb/musb/musb_host.c
>>> +++ b/drivers/usb/musb/musb_host.c
>>> @@ -999,6 +999,8 @@ 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;
>>> +		rx_csr &= ~MUSB_RXCSR_H_REQPKT;
>>> +		musb_writew(epio, MUSB_RXCSR, rx_csr);
>>>  		rx_csr &= ~MUSB_RXCSR_DATAERROR;
>>>  		musb_writew(epio, MUSB_RXCSR, rx_csr);
>>
>>     Can we not clear both in one write?
>
> Section 16.3.8.2.2.1.2 of the TRM says to clear REQPKT before DATAERR_NAKTIMEOUT.

    Right, the MUSB programmer's guide also says that. Then a comment wouldn't 
hurt here.

> Andrew

MBR, Sergei