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 19:46:26 +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 06:19 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.
>>
>>     The full document name is "MUSBMHDRC USB 2.0 HIGH-SPEED DUAL-ROLE
>> CONTROLLER Programmer's Guide".
>
> I moved the comment up to replace the one at the top so the patch now looks like this
>
> 	if (is_in) {
>  		dma = is_dma_capable() ? ep->rx_channel : NULL;
>
> -		/* clear nak timeout bit */
> +		/*
> +		 * Need to stop the transaction by clearing REQPKT first
> +		 * then the NAK Timeout bit ref MUSBMHDRC USB 2.0 HIGH-SPEED
> +		 * DUAL-ROLE CONTROLLER Programmer's Guide, section 9.2.2
> +		 */
>  		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);
>
>
> Are you OK with that now?
> Andrew

    Yes, thank you.

MBR, Sergei