Date: Fri, 15 May 2009 14:16:42 +0400 From: Stanislav Sedov <stas@FreeBSD.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r192027 - head/sys/arm/at91 Message-ID: <20090515141642.ebc06b59.stas@FreeBSD.org> In-Reply-To: <20090514.233536.1299798630.imp@bsdimp.com> References: <200905122114.n4CLEag9033208@svn.freebsd.org> <20090514.213712.-404854369.imp@bsdimp.com> <20090515092205.6f6d06fa.stas@FreeBSD.org> <20090514.233536.1299798630.imp@bsdimp.com>
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On Thu, 14 May 2009 23:35:36 -0600 (MDT) "M. Warner Losh" <imp@bsdimp.com> mentioned: > In message: <20090515092205.6f6d06fa.stas@FreeBSD.org> > Stanislav Sedov <stas@FreeBSD.org> writes: > : On Thu, 14 May 2009 21:37:12 -0600 (MDT) > : "M. Warner Losh" <imp@bsdimp.com> mentioned: > : > : > In message: <200905122114.n4CLEag9033208@svn.freebsd.org> > : > Stanislav Sedov <stas@FreeBSD.org> writes: > : > : @@ -926,6 +937,7 @@ atestart_locked(struct ifnet *ifp) > : > : * tell the hardware to xmit the packet. > : > : */ > : > : WR4(sc, ETH_TAR, segs[0].ds_addr); > : > : + BARRIER(sc, ETH_TAR, 8, BUS_SPACE_BARRIER_WRITE); > : > : WR4(sc, ETH_TCR, segs[0].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. -- Stanislav Sedov ST4096-RIPE !DSPAM:4a0d7946994291610616987!
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