Date: Fri, 20 Nov 2015 09:51:21 +0530 From: prateek sethi <prateekrootkey@gmail.com> To: freebsd-drivers@freebsd.org Subject: Re: freebsd-drivers Digest, Vol 310, Issue 2 Message-ID: <CABD8d0qJ%2Bi%2BVaoOi5Zcjo_7ctjvRbutuSRknWvUpkY4nrnQQvQ@mail.gmail.com> In-Reply-To: <mailman.36.1444392000.41924.freebsd-drivers@freebsd.org>
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Memory barrier On Fri, Oct 9, 2015 at 5:30 PM, <freebsd-drivers-request@freebsd.org> wrote: > Send freebsd-drivers mailing list submissions to > freebsd-drivers@freebsd.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.freebsd.org/mailman/listinfo/freebsd-drivers > or, via email, send a message with subject or body 'help' to > freebsd-drivers-request@freebsd.org > > You can reach the person managing the list at > freebsd-drivers-owner@freebsd.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of freebsd-drivers digest..." > > > Today's Topics: > > 1. Re: Memory barrier (John-Mark Gurney) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 8 Oct 2015 15:39:35 -0700 > From: John-Mark Gurney <jmg@funkthat.com> > To: Leonardo Fogel <leonardofogel@yahoo.com.br> > Cc: freebsd-drivers@freebsd.org > Subject: Re: Memory barrier > Message-ID: <20151008223935.GH67524@funkthat.com> > Content-Type: text/plain; charset=us-ascii > > Leonardo Fogel wrote this message on Sun, Sep 06, 2015 at 06:53 -0700: > > Please, what are the correct barriers for the following cases? > > > > Case 1: > > bus_write_1(region_0, ...); > > /* barrier here */ > > DELAY(some_time); > > > > Case 2: > > bus_write_1(region_0, ...); > > /* barrier here */ > > bus_write_1(region_2, ...); > > > > In the first one, I want the write to reach the device before the thread > busy-waits. As I understand it, bus_space_barrier(9) is not adequate, > because it does not prevent the processor from executing instructions (or > load/store to RAM) before the write completes. > > > > In the second one, I want the write to a device (e.g. power management) > to complete before the write to another starts/completes. Again, > bus_space_barrier() seems not to be adequate because it can not cover two > regions. > > > > Thank you for your time. > > If this is a PCI device, you need to do a read from the device before > it is guaranteed that all the bridges have flushed the writes to the > device... A barrier only guarantees from the processor's perspective > that the write "has completed", but not that it will reach the device.. > > If this is a different bus, then the rules are probably different... > > -- > John-Mark Gurney Voice: +1 415 225 5579 > > "All that I will do, has been done, All that I have, has not." > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > freebsd-drivers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-drivers > To unsubscribe, send any mail to "freebsd-drivers-unsubscribe@freebsd.org" > > ------------------------------ > > End of freebsd-drivers Digest, Vol 310, Issue 2 > *********************************************** >home | help
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