Date: Fri, 25 Sep 1998 11:25:43 -0700 From: Mike Smith <mike@smith.net.au> To: Bill Paul <wpaul@skynet.ctr.columbia.edu> Cc: hackers@FreeBSD.ORG Subject: Re: RealTek + memory mapped registers + SMP == ?*%^(#!! Message-ID: <199809251825.LAA00418@dingo.cdrom.com> In-Reply-To: Your message of "Fri, 25 Sep 1998 12:56:42 EDT." <199809251656.MAA03274@skynet.ctr.columbia.edu>
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> Uhm... this is a question for those with more hardware clues than I.
> Originally I set up the RealTek driver to use PCI memory mapped mode to
> access the chip registers. This worked fine on the development machine
> I used, which is a single processor Dell Optiplex GX1 (PII, 400Mhz).
>
> SMP machines don't seem to like it though. I also have a Dell PowerEdge
> 2300/400 machine (dual PII 400Mhz, 256MB RAM) and on this machine, the
> driver causes the system to lock up when doing certain register access
> operations. It looks like the problem is performing multiple register
> accesses in rapid succession. For example, the first place it locks up
> is when attempting to load the MAC address: there's a small for(;;)
> loop like this:
>
> /* Init our MAC address */
> for (i = 0; i < ETHER_ADDR_LEN; i++) {
> CSR_WRITE_1(sc, RL_IDR0 + i, sc->arpcom.ac_enaddr[i]);
> }
>
> The machine grinds to a halt at this point. The same thing happens
> with a uniprocessor kernel on the same hardware. If I switch to using
> programmed I/O mode, everything works fine. (I updated the driver at
> www.freebsd.org/~wpaul so that PIO mode is now the default.)
>
> Can anyone think of a reason why this would happen? The machine also
> has two Intel EtherExpress Pro 100B adapters, and the fxp driver, which
> also uses memory mapped access, works fine. I suspect that there's
> just something bogus about the RealTek chip that's causing it, but I
> don't know what.
I would hazard a guess that the problem has to do with the fact that
memory operations don't behave the same as I/O operations. It would be
interesting to know if the memory-mapped registers are marked as
"cacheable", or "write-combined".
I doubt, given your colourful descriptions of the RealTek device's
design, whether it would be able to handle memory accesses that didn't
look like I/O accesses (possibly out of order, possibly combined or
part of a cache line writeout if those options were set).
--
\\ Sometimes you're ahead, \\ Mike Smith
\\ sometimes you're behind. \\ mike@smith.net.au
\\ The race is long, and in the \\ msmith@freebsd.org
\\ end it's only with yourself. \\ msmith@cdrom.com
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