On 12/05/2017 08:18 AM, Stefan Wahren wrote:
> Hi Felipe,
> Hi John,
>
>
> Am 30.10.2017 um 18:08 schrieb Douglas Anderson:
>> On rk3288-veyron devices on Chrome OS it was found that plugging in an
>> Arduino-based USB device could cause the system to lockup, especially
>> if the CPU Frequency was at one of the slower operating points (like
>> 100 MHz / 200 MHz).
>>
>> Upon tracing, I found that the following was happening:
>> * The USB device (full speed) was connected to a high speed hub and
>> then to the rk3288. Thus, we were dealing with split transactions,
>> which is all handled in software on dwc2.
>> * Userspace was initiating a BULK IN transfer
>> * When we sent the SSPLIT (to start the split transaction), we got an
>> ACK. Good. Then we issued the CSPLIT.
>> * When we sent the CSPLIT, we got back a NAK. We immediately (from
>> the interrupt handler) started to retry and sent another SSPLIT.
>> * The device kept NAKing our CSPLIT, so we kept ping-ponging between
>> sending a SSPLIT and a CSPLIT, each time sending from the interrupt
>> handler.
>> * The handling of the interrupts was (because of the low CPU speed and
>> the inefficiency of the dwc2 interrupt handler) was actually taking
>> _longer_ than it took the other side to send the ACK/NAK. Thus we
>> were _always_ in the USB interrupt routine.
>> * The fact that USB interrupts were always going off was preventing
>> other things from happening in the system. This included preventing
>> the system from being able to transition to a higher CPU frequency.
>>
>> As I understand it, there is no requirement to retry super quickly
>> after a NAK, we just have to retry sometime in the future. Thus one
>> solution to the above is to just add a delay between getting a NAK and
>> retrying the transmission. If this delay is sufficiently long to get
>> out of the interrupt routine then the rest of the system will be able
>> to make forward progress. Even a 25 us delay would probably be
>> enough, but we'll be extra conservative and try to delay 1 ms (the
>> exact amount depends on HZ and the accuracy of the jiffy and how close
>> the current jiffy is to ticking, but could be as much as 20 ms or as
>> little as 1 ms).
>>
>> Presumably adding a delay like this could impact the USB throughput,
>> so we only add the delay with repeated NAKs.
>>
>> NOTE: Upon further testing of a pl2303 serial adapter, I found that
>> this fix may help with problems there. Specifically I found that the
>> pl2303 serial adapters tend to respond with a NAK when they have
>> nothing to say and thus we end with this same sequence.
>>
>> Signed-off-by: Douglas Anderson <[email protected]>
>> Cc: [email protected]
>> Reviewed-by: Julius Werner <[email protected]>
>> Tested-by: Stefan Wahren <[email protected]>
>> ---
>>
>> Changes in v3:
>> - Add tested-by for Stefan Wahren
>> - Sent to Felipe Balbi as candiate to land this.
>> - Add Cc for stable (it's always been broken so go as far is as easy)
>>
>> Changes in v2:
>> - Address https://urldefense.proofpoint.com/v2/url?u=http-3A__crosreview.com_737520&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=U3o8uKoKhWme5_V9D-eeCkB11BFwt4KvWztBgdE9ZpA&m=Y_xpJ6Ks0XAK5_bQgmeQEvgKThZtPBQJ3cejNCGfEvM&s=olyPwyYvn_072esVwYxrCduKOKKJPUgc1YHX-CNhM1s&e= feedback
>>
>
> does it need a resend?
>
You can add my acked-by:
Acked-by: John Youn <[email protected]>
Regards,
John