linux-kernel - Re: [PATCH v4 1/6] usb: musb: core: Handle Babble condition only in HOST mode

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Date:	Thu, 22 May 2014 15:42:51 -0500
From:	Bin Liu <binmlist@...il.com>
To:	George Cherian <george.cherian@...com>
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-omap@...r.kernel.org, gregkh@...uxfoundation.org,
	balbi@...com, zonque@...il.com, b-liu@...com
Subject: Re: [PATCH v4 1/6] usb: musb: core: Handle Babble condition only in
 HOST mode

Hi George,

On Mon, May 19, 2014 at 11:32 PM, George Cherian <george.cherian@...com> wrote:
> Hi Bin,
>
> On 5/19/2014 9:24 PM, Bin Liu wrote:
>>
>> Hi,
>>
>> On Mon, May 19, 2014 at 8:39 AM, George Cherian <george.cherian@...com>
>> wrote:
>>>
>>> BABBLE and RESET share the same interrupt. The interrupt
>>> is considered to be RESET if MUSB is in peripheral mode and
>>> as a BABBLE if MUSB is in HOST mode.
>>>
>>> Handle babble condition iff MUSB is in HOST mode.
>>>
>>> Signed-off-by: George Cherian <george.cherian@...com>
>>> ---
>>>   drivers/usb/musb/musb_core.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/musb/musb_core.c b/drivers/usb/musb/musb_core.c
>>> index 61da471..eff3c5c 100644
>>> --- a/drivers/usb/musb/musb_core.c
>>> +++ b/drivers/usb/musb/musb_core.c
>>> @@ -849,7 +849,7 @@ b_host:
>>>          }
>>>
>>>          /* handle babble condition */
>>> -       if (int_usb & MUSB_INTR_BABBLE)
>>> +       if (int_usb & MUSB_INTR_BABBLE && is_host_active(musb))
>>>                  schedule_work(&musb->recover_work);
>>
>> I guess my following comments are for Daniel's patch as while which
>> initially added the babble work.
>>
>> Should this if statement be merged into the previous 'if(int_usb &
>> MUSB_INTR_RESET)' one, which handles the same interrupt and already
>> handles host and device mode respectively.
>
>
> Initially I too had the babble handling as part of  'if(int_usb &
> MUSB_INTR_RESET)'
> one. But during my tests I hit a corner case where in we hit a BABBLE
> condition
> on disconnect. In such case the babble interrupt can be handled only if we
> have a seperate
> check, else its considered as a BUS RESET.
>
> When all devices are disconnected  MUSB_DEVCTL_HM = 0 and the code always
> enter the
> else path. In this path it treats the BABBLE as a BUS RESET.

The code flow is a bit confusing, two if() handle the same interrupt.
The second one implied using 'handled = IRQ_HANDLED;' from the first
one.
Also does the switch() in else{} in the first if() cause any side effect?

Since this babble handing is AM335x specific, how about handle it in
dsps_interrupt() in musb_dsps.c, which already has an entry for babble
interrupt? TI 3.2 kernel does this way.

Regards,
-Bin.

>
>
>> Regards,
>> -Bin.
>>
>>>   #if 0
>>> --
>>> 1.8.3.1
>>>
>>> --
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>
>
>
> --
> -George
>
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