svn commit: r192027 - head/sys/arm/at91
stas at FreeBSD.org
Fri May 15 14:22:08 UTC 2009
On Thu, 14 May 2009 23:35:36 -0600 (MDT)
"M. Warner Losh" <imp at bsdimp.com> mentioned:
> In message: <20090515092205.6f6d06fa.stas at FreeBSD.org>
> Stanislav Sedov <stas at FreeBSD.org> writes:
> : On Thu, 14 May 2009 21:37:12 -0600 (MDT)
> : "M. Warner Losh" <imp at bsdimp.com> mentioned:
> : > In message: <200905122114.n4CLEag9033208 at svn.freebsd.org>
> : > Stanislav Sedov <stas at FreeBSD.org> writes:
> : > : @@ -926,6 +937,7 @@ atestart_locked(struct ifnet *ifp)
> : > : * tell the hardware to xmit the packet.
> : > : */
> : > : WR4(sc, ETH_TAR, segs.ds_addr);
> : > : + BARRIER(sc, ETH_TAR, 8, BUS_SPACE_BARRIER_WRITE);
> : > : WR4(sc, ETH_TCR, segs.ds_len);
> : >
> : > Why is a barrier needed here?
> : >
> : Writing the TCR register triggers the transmit, so it had to be written
> : strongly after the TAR register. That's why I added the barrier here.
> Then shouldn't the barrier be after TCR write? Or does this ensure
> that the write is before TCR?
Yeah, this barrier is to ensure that the TCR register gets written after the
TAR register has been written, not before. I don't think an additional barrier
is needed after the TCR write.
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