gprs: Fix LLC UI window
According to TS 44.064 section 8.4.2, the LLC layer should only drop UI frames if V(UR)-32 <= N(U) < V(UR). The code was dropping frames whenever N(U) < V(UR). Consequently, large amounts of packets could be dropped if, e.g., V(UR)==511 and the frame with N(U)==511 was lost. All frames would be dropped until the next time a frame with N(U)==511 is received.
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@ -482,17 +482,21 @@ static int gprs_llc_hdr_rx(struct gprs_llc_hdr_parsed *gph,
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}
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break;
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case GPRS_LLC_UI:
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if (gph->seq_tx < lle->vu_recv) {
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{
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int delta = (lle->vu_recv - gph->seq_tx) & 0x1ff;
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if (0 < delta && delta < 32) {
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LOGP(DLLC, LOGL_NOTICE, "TLLI=%08x dropping UI, vurecv %u <= %u\n",
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lle->llme ? lle->llme->tlli : -1,
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gph->seq_tx, lle->vu_recv);
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return -EIO;
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}
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/* Increment the sequence number that we expect in the next frame */
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lle->vu_recv = (gph->seq_tx + 1) % 512;
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lle->vu_recv = (gph->seq_tx + 1) & 0x1ff;
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/* Increment Overflow Counter */
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if ((gph->seq_tx + 1) / 512)
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if (lle->vu_recv == 0) {
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lle->oc_ui_recv += 512;
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}
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}
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break;
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}
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