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SubjectRe: [PATCH V2 2/2] usb: musb: Stop bulk endpoint while queue is rotated
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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@cambrionix.com>
>>> Cc: stable@vger.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

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