> -----Original Message-----
> From: Felipe Balbi <felipe.ba...@linux.intel.com>
> Sent: Friday, June 7, 2019 2:50 AM
> To: John Youn <john.y...@synopsys.com>
> Cc: linux-usb@vger.kernel.org
> Subject: [RFC] Sorting out dwc3 ISOC endpoints once and for all
>
++ Thinh
Hi Felipe,
Sorry, missed this e-mail.
> Now that we have dwc3_gadget_start_isoc_quirk() which figures out the
> correct combination for the top-most 2 bits in the frame number, why
> don't we just use that to start isochronous transfers and never, again,
> have Bus Expiry problems?
We should only see expiry problems on the affected versions with incorrect
top-2 bits right?
>
> I mean something along the lines of below diff (completely untested):
>
> modified drivers/usb/dwc3/gadget.c
> @@ -1369,9 +1369,8 @@ static int dwc3_gadget_start_isoc_quirk(struct
> dwc3_ep *dep)
> else if (test0 && test1)
> dep->combo_num = 0;
>
> - dep->frame_number &= 0x3fff;
> dep->frame_number |= dep->combo_num << 14;
> - dep->frame_number += max_t(u32, 4, dep->interval);
> + dep->frame_number = DWC3_ALIGN_FRAME(dep, 1);
>
> /* Reinitialize test variables */
> dep->start_cmd_status = 0;
> @@ -1383,33 +1382,16 @@ static int dwc3_gadget_start_isoc_quirk(struct
> dwc3_ep *dep)
> static int __dwc3_gadget_start_isoc(struct dwc3_ep *dep)
> {
> struct dwc3 *dwc = dep->dwc;
> - int ret;
> - int i;
>
> if (list_empty(&dep->pending_list)) {
> dep->flags |= DWC3_EP_PENDING_REQUEST;
> return -EAGAIN;
> }
>
> - if (!dwc->dis_start_transfer_quirk && dwc3_is_usb31(dwc) &&
> - (dwc->revision <= DWC3_USB31_REVISION_160A ||
> - (dwc->revision == DWC3_USB31_REVISION_170A &&
> - dwc->version_type >= DWC31_VERSIONTYPE_EA01 &&
> - dwc->version_type <= DWC31_VERSIONTYPE_EA06))) {
> -
> - if (dwc->gadget.speed <= USB_SPEED_HIGH && dep->direction)
> - return dwc3_gadget_start_isoc_quirk(dep);
> - }
> -
> - for (i = 0; i < DWC3_ISOC_MAX_RETRIES; i++) {
> - dep->frame_number = DWC3_ALIGN_FRAME(dep, i + 1);
> + dep->frame_number = __dwc3_gadget_get_frame(dwc);
> + dep->frame_number = DWC3_ALIGN_FRAME(dep, 1);
>
> - ret = __dwc3_gadget_kick_transfer(dep);
> - if (ret != -EAGAIN)
> - break;
> - }
> -
> - return ret;
> + return dwc3_gadget_start_isoc_quirk(dep);
> }
>
> static int __dwc3_gadget_ep_queue(struct dwc3_ep *dep, struct
> dwc3_request *req)
>
>
> Would there be any obvious draw-back to going down this route? The thing
> is that, as it is, it seems like we will *always* have some corner case
> where we can't guarantee that we can even start a transfer since there's
> no upper-bound between XferNotReady and gadget driver finally queueing a
> request. Also, I can't simply read DSTS for the frame number because of
> top-most 2 bits.
>
For non-affected version of the IP, the xfernotready -> starttransfer time will
have to be off by more than a couple seconds for the driver to produce an
incorrect 16-bit frame number. If you're seeing errors here, maybe we just need
to code review the relevant sections to make sure the 14/16-bit and rollover
conditions are all handled correctly.
But I can't think of any obvious drawbacks of the quirk, other than doing some
unnecessary work, which shouldn't produce any bad side-effects. But we haven't
really tested that.
John
