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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Message-ID: <BL0PR02MB56331B2ECFFEB96A99936C32A7AB0@BL0PR02MB5633.namprd02.prod.outlook.com>
Date:   Sat, 8 Dec 2018 19:03:33 +0000
From:   Anurag Kumar Vulisha <anuragku@...inx.com>
To:     Felipe Balbi <balbi@...nel.org>,
        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" <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-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "v.anuragkumar@...il.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 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.
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.

@@ -998,7 +998,7 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep *dep, struct dwc3_trb *trb,
                        (dwc3_calc_trbs_left(dep) == 1))
                trb->ctrl |= DWC3_TRB_CTRL_IOC;
 
-       if (chain)
+       if (chain && !(trb->ctrl & DWC3_TRB_CTRL_IOC))
                trb->ctrl |= DWC3_TRB_CTRL_CHN;
 
        if (usb_endpoint_xfer_bulk(dep->endpoint.desc) && dep->stream_capable)
@@ -2372,7 +2372,7 @@ 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)
+       if (event->status & DEPEVT_STATUS_IOC && !chain)
                return 1;
 
        return 0;
@@ -2399,7 +2399,7 @@ static int dwc3_gadget_ep_reclaim_trb_sg(struct dwc3_ep *dep,
                req->num_pending_sgs--;
 
                ret = dwc3_gadget_ep_reclaim_completed_trb(dep, req,
-                               trb, event, status, true);
+                               trb, event, status, (trb & DWC3_TRB_CTRL_CHN));
                if (ret)
                        break;
        }

Thanks,
Anurag Kumar Vulisha

>modified   drivers/usb/dwc3/gadget.c
>@@ -2372,7 +2372,7 @@ 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)
>+	if (event->status & DEPEVT_STATUS_IOC && !chain)
> 		return 1;
>
> 	return 0;
>
>--
>balbi