Question about be2net error field, rx_drops_no_pbuf

Hi,

What does 'rx_drops_no_pbuf' mean at be2net driver? I can see it is a 
hardware counter for some type of error, which I would like to know 
about. What causes it?

All documentation I could find about it is a comment referring firmware 
specification:

struct be_rxf_stats_v0 {
     struct be_port_rxf_stats_v0 port[2];
     u32 rx_drops_no_pbuf;   /* dword 132*/
     ...
}

struct be_rxf_stats_v1 {
     struct be_port_rxf_stats_v1 port[4];
     u32 rsvd0[2];
     u32 rx_drops_no_pbuf;
     ...
}

That, plus this:

be_get_stats64()
{
     ...
     /* receiver fifo overrun */
     /* drops_no_pbuf is no per i/f, it's per BE card */
     stats->rx_fifo_errors = drvs->rxpp_fifo_overflow_drop +
                 drvs->rx_input_fifo_overflow_drop +
                 drvs->rx_drops_no_pbuf;
     return stats;
}

Thanks,
Marcelo.