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Date:   Mon, 1 Feb 2010 14:50:27 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@linux-mips.org>
To:     Ralf Baechle <ralf@linux-mips.org>
cc:     Guenter Roeck <guenter.roeck@ericsson.com>,
        David Daney <ddaney@caviumnetworks.com>,
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Subject: Re: Kernel crash in 2.6.32.6 / bcm1480 with 16k page size
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On Mon, 1 Feb 2010, Ralf Baechle wrote:

> Write a value with all bits set to c0_entryhi, then read it back again.
> The set bits in the VPN2 bitfield will indicate the size of the virtual
> address range supported.  The MIPS64 documentation also calls this value
> SEGBITS.  The nice thing about this probe is that it is supported for
> all 64-bit MIPS processors except the R8000 which has an entirely different
> TLB scheme anyway.
> 
> Similarly it is possible to probe the physical address range in either
> c0_entrylo0 or c0_entrylo1.  This is also of interest on 32-bit processors.

 Indeed -- IIRC the architecture spec calls this value PABITS.  I wasn't 
sure about the legacy processors -- if that works with them too, then it's 
even better.

  Maciej