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 <dianders@xxxxxxxxxxxx> >> Cc: stable@xxxxxxxxxxxxxxx >> Reviewed-by: Julius Werner <jwerner@xxxxxxxxxxxx> >> Tested-by: Stefan Wahren <stefan.wahren@xxxxxxxx> >> --- >> >> 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 <johnyoun@xxxxxxxxxxxx> Regards, John