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

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Message-ID: <c63488a8-321d-49f4-8efa-67c8d8dad488@cogentembedded.com>
Date:	Mon, 23 May 2016 16:40:17 +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 V2 2/2] usb: musb: Stop bulk endpoint while queue is
 rotated

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@...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.

    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