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Re: [PATCH] MIPS: Calculate proper ebase value for 64-bit kernels

To:, Ralf Baechle <>
Subject: Re: [PATCH] MIPS: Calculate proper ebase value for 64-bit kernels
From: David Daney <>
Date: Mon, 26 Apr 2010 17:22:16 -0700
Cc: linux-mips <>
In-reply-to: <Pine.LNX.4.21.1004270049440.1248-100000@Mobile0.Peter>
Original-recipient: rfc822;
References: <Pine.LNX.4.21.1004270049440.1248-100000@Mobile0.Peter>
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On 04/26/2010 06:25 PM, wrote:

Hi David,

please excuse me, i just couldn't resist to comment on this :-)

Some time ago we needed to handle multiple (virtual) address-spaces
(in TO_CAC/TO_UNCAC as well as in virt_to_phys and the like) for
SGI's Indigo2/R10k and Octane (neither could run a 32bit kernel).
So in addrspace.h we provided
        #ifdef CONFIG_64BIT
        static inline unsigned long kernel_physaddr(unsigned long kva)
                        return CPHYSADDR(kva);
                return XPHYSADDR(kva);
        #define kernel_physaddr CPHYSADDR
while mach-ipXX/spaces.h defined
        #define TO_PHYS(x)      (             kernel_physaddr(x))
        #define TO_CAC(x)       (CAC_BASE   | kernel_physaddr(x))
        #define TO_UNCAC(x)     (UNCAC_BASE | kernel_physaddr(x))
which did the job.
But at that time these defines didn't meet much acceptance for general
use in 64bit kernels.  Now, to my amusement, some modern processor
(and/or system) seems to urge this kind of address-handling again  ;-)

FWIW, that seems cleaner than what I did (actually I didn't try my code). That should be the default definition for 64-bit kernels I think.

David Daney

Good luck!

On Mon, 26 Apr 2010, David Daney wrote:

Date: Mon, 26 Apr 2010 10:19:04 -0700
From: David Daney<>
Cc: Ralf Baechle<>,
      Thomas Bogendoerfer<>,
Subject: Re: [PATCH] MIPS: Calculate proper ebase value for 64-bit kernels

I don't think so.  We should fix TO_UNCAC() so that it works with CKSEG0
addresses.  It should be at physical address 0.  So
TO_UNCAC(0xffffffff80000000), should yield 0x9000000000000000

#define TO_UNCAC(x) ({ \
        u64 a = (u64)(x);     \
        if (a&  0xffffffffc000000 == 0xffffffff80000000) \
                a = UNCAC_BASE | (a&  0x30000000); \
        else \
                a = UNCAC_BASE | (a&  TO_PHYS_MASK) \
        a; \

David Daney


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