Re: [PATCH v2 2/2] usb: dwc2: fix isoc split in transfer with no data

[wlf <wulf@rock-chips.com>]

Dear Doug,


在 2018年05月02日 13:02, Doug Anderson 写道:
> Hi,
>
> On Tue, May 1, 2018 at 8:04 PM, William Wu <william.wu@rock-chips.com> wrote:
>> If isoc split in transfer with no data (the length of DATA0
>> packet is zero), we can't simply return immediately. Because
>> the DATA0 can be the first transaction or the second transaction
>> for the isoc split in transaction. If the DATA0 packet with no
>> data is in the first transaction, we can return immediately.
>> But if the DATA0 packet with no data is in the second transaction
>> of isoc split in transaction sequence, we need to increase the
>> qtd->isoc_frame_index and giveback urb to device driver if needed,
>> otherwise, the MDATA packet will be lost.
>>
>> A typical test case is that connect the dwc2 controller with an
>> usb hs Hub (GL852G-12), and plug an usb fs audio device (Plantronics
>> headset) into the downstream port of Hub. Then use the usb mic
>> to record, we can find noise when playback.
>>
>> In the case, the isoc split in transaction sequence like this:
>>
>> - SSPLIT IN transaction
>> - CSPLIT IN transaction
>>    - MDATA packet (176 bytes)
>> - CSPLIT IN transaction
>>    - DATA0 packet (0 byte)
>>
>> This patch use both the length of DATA0 and qtd->isoc_split_offset
>> to check if the DATA0 is in the second transaction.
>>
>> Signed-off-by: William Wu <william.wu@rock-chips.com>
>> ---
>> Changes in v2:
>> - Modify the commit message
>>
>>   drivers/usb/dwc2/hcd_intr.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc2/hcd_intr.c b/drivers/usb/dwc2/hcd_intr.c
>> index 5e2378f..479f628 100644
>> --- a/drivers/usb/dwc2/hcd_intr.c
>> +++ b/drivers/usb/dwc2/hcd_intr.c
>> @@ -930,7 +930,7 @@ static int dwc2_xfercomp_isoc_split_in(struct dwc2_hsotg *hsotg,
>>          frame_desc = &qtd->urb->iso_descs[qtd->isoc_frame_index];
>>          len = dwc2_get_actual_xfer_length(hsotg, chan, chnum, qtd,
>>                                            DWC2_HC_XFER_COMPLETE, NULL);
>> -       if (!len) {
>> +       if (!len && !qtd->isoc_split_offset) {
>>                  qtd->complete_split = 0;
>>                  qtd->isoc_split_offset = 0;
>>                  return 0;
> I don't think my USB-fu is strong enough to do a real review of this
> patch, but one small nitpick is that you can remove
> "qtd->isoc_split_offset = 0" in the if test now.  AKA:
>
> if (!len && !qtd->isoc_split_offset) {
>    qtd->complete_split = 0;
>    return 0;
> }
Yes, good idea! I will fix it in next patch. Thank you!
>
> ...since you only enter the "if" test now when isoc_split_offset is
> already 0...  Hopefully John Youn will have some time to comment on
> this patch with more real USB knowledge...
>
>
> -Doug
>
Best regards,
      wulf
>