From owner-freebsd-ports  Tue Mar 27 23: 0: 7 2001
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Date: Tue, 27 Mar 2001 23:00:04 -0800 (PST)
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From: natedac@kscable.com
Subject: Re: ports/25958: Xfree86's savage and vesa drivers%2
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The following reply was made to PR ports/25958; it has been noted by GNATS.

From: natedac@kscable.com
To: freebsd-gnats-submit@FreeBSD.org, natedac@kscable.com
Cc: natedac@kscable.com, jhb@FreeBSD.org
Subject: Re: ports/25958: Xfree86's savage and vesa drivers%2
Date: Wed, 28 Mar 2001 00:51:49 -0600 (CST)

 Thanks to lots of help from BigSpoon on #BSDcode/EFnet (jhb@FreeBSD.org),
 here's a more proper way to fix the MTRR problem that plages some machines
 like mine.  This will allow the MTRR support to be disabled at will either
 in /boot/loader.conf or at the boot prompt.  It appears that today the
 copy of this file sitting on ftp.freebsd.org has been changed slightly (so
 a patch/diff against my week-old copy would be of little use anyways ;-)
 
 Anyways, here we go:
 
 Edit /usr/src/sys/i386/i386/i686_mem.c
 
 Somewhere near the start of the file, add these two lines:
 
 ------------------------------------------------------------------------------
    static int mtrrs_disabled;
    TUNABLE_INT_DECL("machdep.mtrrs_disabled", 0, mtrrs_disabled);
 ------------------------------------------------------------------------------
 
 Then, go to the end of the file, and make these changes to 
 i686_mem_drvinit()...
 
 ------------------------------------------------------------------------------
    static void
    i686_mem_drvinit(void *unused)
 
    {
 
    /* First, check if the user wants to allow MTRR at all */
 
    if (mtrrs_disabled) { return; }
 
        /* Ok, MTRR is allowed, so try for i686 MTRRs */
 
        if ((cpu_feature & CPUID_MTRR) &&
           ((cpu_id & 0xf00) == 0x600) &&
           ((strcmp(cpu_vendor, "GenuineIntel") == 0) ||
           (strcmp(cpu_vendor, "AuthenticAMD") == 0))) {
           mem_range_softc.mr_op = &i686_mrops;
        }
    }
 -----------------------------------------------------------------------------
 
 Finally, add a line to /boot/loader.conf to disable the MTRR support if 
 you need to (leaving it out or mis-spelling the variable name will cause 
 MTRR support to be detected and enabled normally):
 
 machdep.mtrrs_disabled = 1
 
 I guess at this point, the original PR should remain open until the bug is
 solved in a more formal manner, but this seems to be an effective
 workaround.  So far, I haven't seen any ill effects from disabling MTRR's.

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