> [from old commit log]
> 
> In article <20050323202308.2BDE62DA27@cvs.netbsd.org>
> yamt@netbsd.org wrote:
> 
> > Module Name:	src
> > Committed By:	yamt
> > Date:		Wed Mar 23 20:23:08 UTC 2005
> > 
> > Modified Files:
> > 	src/sys/dev/ic: rtl8169.c rtl81x9reg.h rtl81x9var.h
> > 
> > Log Message:
> > - restructure tx descriptor handling code to decouple
> >   number of tx descriptors, number of rx descriptors, and number of mbufs.
> > - bump number of tx descriptors for rtl8169.  64 doesn't seem to be sufficient
> >   when doing TSO.
> 
> 
> >>+	if (sc->rtk_ldata.rtk_tx_desc_cnt >
> >>+	    PAGE_SIZE / sizeof(struct rtk_desc)) {
> >>+		sc->rtk_ldata.rtk_tx_desc_cnt =
> >>+		    PAGE_SIZE / sizeof(struct rtk_desc);
> >>+	}
> 
> Is there any reason to limit a number of TX descriptors by PAGE_SIZE?
> (it's limited to 256 on 4KB/page system)
> 
> Other drivers have more descriptors, for example, tlp(4) has 1024,
> and ex(4) uses >64KB DMA memory for TX descriptors.
> ---
> Izumi Tsutsui

i don't remember, sorry.

maybe because contiguous page allocation likely fails when
the device is hot-plugged?  (i was using re@cardbus at that time.)

YAMAMOTO Takashi