From owner-freebsd-mips@FreeBSD.ORG  Fri Sep 10 07:07:08 2010
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From: Juli Mallett <jmallett@FreeBSD.org>
Date: Fri, 10 Sep 2010 00:06:46 -0700
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To: "Jayachandran C." <c.jayachandran@gmail.com>
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Cc: gonzo@freebsd.org, freebsd-mips@freebsd.org
Subject: Re: busdma_machdep.c with more than 512M memory
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On Fri, Sep 10, 2010 at 00:00, Jayachandran C. <c.jayachandran@gmail.com> wrote:
> On Fri, Sep 10, 2010 at 11:22 AM, Neel Natu <neelnatu@gmail.com> wrote:
>> This assumes that pmap_mapdev() always returns an uncached mapping
>> which is true for n64 kernels but not for o32 kernels with memory
>> beyond 512MB.
>
> I think my original patch was incorrect, pmap_mapdev() should not be
> used to map physical memory uncached. It may be just for mapping
> device address space uncached, and that may be why it checks if the
> physical address is cacheable.

I think that's a wrong inference from the brokenness of pmap_mapdev
because of using the general-purpose pmap_kenter.  pmap_mapdev is
implicitly uncacheable -- check i386 pmap for confirmation.  Neel's
patch is right.