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

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Date:   Mon, 10 Dec 2018 08:54:13 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Anurag Kumar Vulisha <anuragku@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Johan Hovold <johan@...nel.org>,
        Jaejoong Kim <climbbb.kim@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Roger Quadros <rogerq@...com>,
        Manu Gautam <mgautam@...eaurora.org>,
        "martin.petersen\@oracle.com" <martin.petersen@...cle.com>,
        Bart Van Assche <bvanassche@....org>,
        Mike Christie <mchristi@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Colin Ian King <colin.king@...onical.com>
Cc:     "linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "v.anuragkumar\@gmail.com" <v.anuragkumar@...il.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.com>,
        Ajay Yugalkishore Pandey <APANDEY@...inx.com>
Subject: RE: [PATCH v7 09/10] usb: dwc3: Check for IOC/LST bit in both event->status and TRB->ctrl fields


Hi,

Anurag Kumar Vulisha <anuragku@...inx.com> writes:
> HI Felipe,
>
>>-----Original Message-----
>>From: Felipe Balbi [mailto:balbi@...nel.org]
>>Sent: Friday, December 07, 2018 11:42 AM
>>To: Anurag Kumar Vulisha <anuragku@...inx.com>; Greg Kroah-Hartman
>><gregkh@...uxfoundation.org>; Shuah Khan <shuah@...nel.org>; Alan Stern
>><stern@...land.harvard.edu>; Johan Hovold <johan@...nel.org>; Jaejoong Kim
>><climbbb.kim@...il.com>; Benjamin Herrenschmidt <benh@...nel.crashing.org>;
>>Roger Quadros <rogerq@...com>; Manu Gautam <mgautam@...eaurora.org>;
>>martin.petersen@...cle.com; Bart Van Assche <bvanassche@....org>; Mike
>>Christie <mchristi@...hat.com>; Matthew Wilcox <willy@...radead.org>; Colin Ian
>>King <colin.king@...onical.com>
>>Cc: linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org;
>>v.anuragkumar@...il.com; Thinh Nguyen <thinhn@...opsys.com>; Tejas Joglekar
>><tejas.joglekar@...opsys.com>; Ajay Yugalkishore Pandey <APANDEY@...inx.com>
>>Subject: RE: [PATCH v7 09/10] usb: dwc3: Check for IOC/LST bit in both event->status
>>and TRB->ctrl fields
>>
>>
>>Hi,
>>
>>Anurag Kumar Vulisha <anuragku@...inx.com> 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
>>unhandled.
>>> 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.

-- 
balbi

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