On 04/21/15 05:04, Tian, Feng wrote:
> Baranee & Laszlo,
>
> I agree this is a bug and I made a unit test on this logic and found why this
> issue didn't get raised before is because Fat&DiskIo driver will split big
> data transfer request (>64K) to multiple of 64K. This way will cause a
> request, that is a URB, only needs a transfer TRB, so it will not return
> wrong completed data length as the Urb->DataLen is only accumulated once for
> every URB request.
>
> But if a URB request needs multiple TRBs, then the Urb->Completed is
> calculated wrongly.
>
> Here is my proposed fix, could you help review it?
>
> Index: XhciSched.c
> ===================================================================
> --- XhciSched.c (revision 17189)
> +++ XhciSched.c (working copy)
> @@ -1137,7 +1137,7 @@
> if ((TRBType == TRB_TYPE_DATA_STAGE) ||
> (TRBType == TRB_TYPE_NORMAL) ||
> (TRBType == TRB_TYPE_ISOCH)) {
> - CheckedUrb->Completed += (CheckedUrb->DataLen - EvtTrb->Lenth);
> + CheckedUrb->Completed += (((TRANSFER_TRB_NORMAL*)TRBPtr)->Length -
> EvtTrb->Lenth);
> }
>
> The TRBPtr->Length field means expected transfer length, and the
> EvtTrb->Lenth means the residual number of bytes not transferred.
Can you please explain why "EvtTrb->Lenth" is the residue (ie. the
number of bytes *not* transferred) instead of the number of bytes that
have been transferred?
My understanding would be helped most if you could provide:
- an explanation of the code that implies this (it's quite complicated
code...)
- and a reference from the XHCI spec that the code implements.
I'm asking because (as I wrote earlier) the XHCI spec defines
EvtTrb->Lenth with different meanings in different contexts. In some
contexts it is indeed a residue, but in other contexts EvtTrb->Lenth is
the number of bytes actually transferred. I'm unsure which case we have
at hand.
Thanks!
Laszlo
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