RE: [PATCH v7 09/10] usb: dwc3: Check for IOC/LST bit in both event->status and TRB->ctrl fields

From: Felipe Balbi
Date: Mon Dec 10 2018 - 01:54:38 EST


Anurag Kumar Vulisha <anuragku@xxxxxxxxxx> writes:
> HI Felipe,
>>-----Original Message-----
>>From: Felipe Balbi [mailto:balbi@xxxxxxxxxx]
>>Sent: Friday, December 07, 2018 11:42 AM
>>To: Anurag Kumar Vulisha <anuragku@xxxxxxxxxx>; Greg Kroah-Hartman
>><gregkh@xxxxxxxxxxxxxxxxxxx>; Shuah Khan <shuah@xxxxxxxxxx>; Alan Stern
>><stern@xxxxxxxxxxxxxxxxxxx>; Johan Hovold <johan@xxxxxxxxxx>; Jaejoong Kim
>><>; Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>;
>>Roger Quadros <rogerq@xxxxxx>; Manu Gautam <mgautam@xxxxxxxxxxxxxx>;
>>martin.petersen@xxxxxxxxxx; Bart Van Assche <bvanassche@xxxxxxx>; Mike
>>Christie <mchristi@xxxxxxxxxx>; Matthew Wilcox <willy@xxxxxxxxxxxxx>; Colin Ian
>>King <colin.king@xxxxxxxxxxxxx>
>>Cc: linux-usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>>v.anuragkumar@xxxxxxxxx; Thinh Nguyen <thinhn@xxxxxxxxxxxx>; Tejas Joglekar
>><tejas.joglekar@xxxxxxxxxxxx>; Ajay Yugalkishore Pandey <APANDEY@xxxxxxxxxx>
>>Subject: RE: [PATCH v7 09/10] usb: dwc3: Check for IOC/LST bit in both event->status
>>and TRB->ctrl fields
>>Anurag Kumar Vulisha <anuragku@xxxxxxxxxx> writes:
>>>>> @@ -2286,7 +2286,12 @@ static int
>>>>dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
>>>>> if (event->status & DEPEVT_STATUS_SHORT && !chain)
>>>>> return 1;
>>>>> - if (event->status & (DEPEVT_STATUS_IOC | DEPEVT_STATUS_LST))
>>>>> + if ((event->status & DEPEVT_STATUS_IOC) &&
>>>>> + (trb->ctrl & DWC3_TRB_CTRL_IOC))
>>>>> + return 1;
>>>>this shouldn't be necessary. According to databook, event->status
>>>>contains the bits from the completed TRB. Which means that
>>>>event->status & IOC will always be equal to trb->ctrl & IOC.
>>> Thanks for reviewing this patch. Lets consider an example where a
>>> request has num_sgs > 0 and each sg is mapped to a TRB and the last
>>> TRB has the IOC bit set. Once the controller is done with the
>>> transfer, it generates XferInProgress for the last TRB (since IOC bit
>>> is set). As a part of trb reclaim process
>>> dwc3_gadget_ep_reclaim_trb_sg() calls
>>> dwc3_gadget_ep_reclaim_completed_trb() for req->num_sgs times. Since
>>> the event already has the IOC bit set, the loop is exited from the
>>> loop at the very first TRB and the remaining TRBs (mapped to the sglist) are left
>>> To avoid this we modified the code to exit only if both TRB & event
>>> has the IOC bit set.
>>Seems like IOC case should just test for chain flag as well:
> Okay. Along with this logic the code for updating chain bit should also be modified I guess.

not really

> Since the IOC bit is also set when there are not enough TRBs available, the code should be
> modified to not set DWC3_TRB_CTRL_CHN bit when the IOC bit is set. I will update below
> changes along with your suggestions and resend the patches.

no. Actually I don't think we're allowed to split a scatter/gather like
that. I did that quite a while ago, but I don't think we're allowed to
do so. What we should do, in that case, is not even queue that request
until we have enough for all members of the scatter/gather. But that's a
separate patch, anyway.


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