net/sfc/base: clarify meaning of Rx desc lbits in PS mode

[dpdk.git] / drivers / net / sfc / base / ef10_ev.c

diff --git a/drivers/net/sfc/base/ef10_ev.c b/drivers/net/sfc/base/ef10_ev.c
index eb9ec75..9ed22f8 100644 (file)
--- a/drivers/net/sfc/base/ef10_ev.c
+++ b/drivers/net/sfc/base/ef10_ev.c
@@ -774,7 +774,7 @@ ef10_ev_rx_packed_stream(
        __in_opt        void *arg)
 {
        uint32_t label;
-       uint32_t next_read_lbits;
+       uint32_t pkt_count_lbits;
        uint16_t flags;
        boolean_t should_abort;
        efx_evq_rxq_state_t *eersp;
@@ -782,15 +782,22 @@ ef10_ev_rx_packed_stream(
        unsigned int current_id;
        boolean_t new_buffer;
 
-       next_read_lbits = EFX_QWORD_FIELD(*eqp, ESF_DZ_RX_DSC_PTR_LBITS);
+       pkt_count_lbits = EFX_QWORD_FIELD(*eqp, ESF_DZ_RX_DSC_PTR_LBITS);
        label = EFX_QWORD_FIELD(*eqp, ESF_DZ_RX_QLABEL);
        new_buffer = EFX_QWORD_FIELD(*eqp, ESF_DZ_RX_EV_ROTATE);
 
        flags = 0;
 
        eersp = &eep->ee_rxq_state[label];
-       pkt_count = (EFX_MASK32(ESF_DZ_RX_DSC_PTR_LBITS) + 1 +
-           next_read_lbits - eersp->eers_rx_stream_npackets) &
+
+       /*
+        * RX_DSC_PTR_LBITS has least significant bits of the global
+        * (not per-buffer) packet counter. It is guaranteed that
+        * maximum number of completed packets fits in lbits-mask.
+        * So, modulo lbits-mask arithmetic should be used to calculate
+        * packet counter increment.
+        */
+       pkt_count = (pkt_count_lbits - eersp->eers_rx_stream_npackets) &
            EFX_MASK32(ESF_DZ_RX_DSC_PTR_LBITS);
        eersp->eers_rx_stream_npackets += pkt_count;