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

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Date:	Mon, 23 May 2016 17:37:03 +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 05/23/2016 04:40 PM, Sergei Shtylyov 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.

    The full document name is "MUSBMHDRC USB 2.0 HIGH-SPEED DUAL-ROLE 
CONTROLLER Programmer’s Guide".

>> Andrew
>>
>>> [...]

MBR, Sergei