linux/arch/powerpc
Suzuki Poulose 368ff8f14d powerpc: Define virtual-physical translations for RELOCATABLE
We find the runtime address of _stext and relocate ourselves based
on the following calculation.

	virtual_base = ALIGN(KERNELBASE,KERNEL_TLB_PIN_SIZE) +
			MODULO(_stext.run,KERNEL_TLB_PIN_SIZE)

relocate() is called with the Effective Virtual Base Address (as
shown below)

            | Phys. Addr| Virt. Addr |
Page        |------------------------|
Boundary    |           |            |
            |           |            |
            |           |            |
Kernel Load |___________|_ __ _ _ _ _|<- Effective
Addr(_stext)|           |      ^     |Virt. Base Addr
            |           |      |     |
            |           |      |     |
            |           |reloc_offset|
            |           |      |     |
            |           |      |     |
            |           |______v_____|<-(KERNELBASE)%TLB_SIZE
            |           |            |
            |           |            |
            |           |            |
Page        |-----------|------------|
Boundary    |           |            |

On BookE, we need __va() & __pa() early in the boot process to access
the device tree.

Currently this has been defined as :

#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) -
						PHYSICAL_START + KERNELBASE)
where:
 PHYSICAL_START is kernstart_addr - a variable updated at runtime.
 KERNELBASE	is the compile time Virtual base address of kernel.

This won't work for us, as kernstart_addr is dynamic and will yield different
results for __va()/__pa() for same mapping.

e.g.,

Let the kernel be loaded at 64MB and KERNELBASE be 0xc0000000 (same as
PAGE_OFFSET).

In this case, we would be mapping 0 to 0xc0000000, and kernstart_addr = 64M

Now __va(1MB) = (0x100000) - (0x4000000) + 0xc0000000
		= 0xbc100000 , which is wrong.

it should be : 0xc0000000 + 0x100000 = 0xc0100000

On platforms which support AMP, like PPC_47x (based on 44x), the kernel
could be loaded at highmem. Hence we cannot always depend on the compile
time constants for mapping.

Here are the possible solutions:

1) Update kernstart_addr(PHSYICAL_START) to match the Physical address of
compile time KERNELBASE value, instead of the actual Physical_Address(_stext).

The disadvantage is that we may break other users of PHYSICAL_START. They
could be replaced with __pa(_stext).

2) Redefine __va() & __pa() with relocation offset

#ifdef	CONFIG_RELOCATABLE_PPC32
#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) - PHYSICAL_START + (KERNELBASE + RELOC_OFFSET)))
#define __pa(x) ((unsigned long)(x) + PHYSICAL_START - (KERNELBASE + RELOC_OFFSET))
#endif

where, RELOC_OFFSET could be

  a) A variable, say relocation_offset (like kernstart_addr), updated
     at boot time. This impacts performance, as we have to load an additional
     variable from memory.

		OR

  b) #define RELOC_OFFSET ((PHYSICAL_START & PPC_PIN_SIZE_OFFSET_MASK) - \
                      (KERNELBASE & PPC_PIN_SIZE_OFFSET_MASK))

   This introduces more calculations for doing the translation.

3) Redefine __va() & __pa() with a new variable

i.e,

#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + VIRT_PHYS_OFFSET))

where VIRT_PHYS_OFFSET :

#ifdef CONFIG_RELOCATABLE_PPC32
#define VIRT_PHYS_OFFSET virt_phys_offset
#else
#define VIRT_PHYS_OFFSET (KERNELBASE - PHYSICAL_START)
#endif /* CONFIG_RELOCATABLE_PPC32 */

where virt_phy_offset is updated at runtime to :

	Effective KERNELBASE - kernstart_addr.

Taking our example, above:

virt_phys_offset = effective_kernelstart_vaddr - kernstart_addr
		 = 0xc0400000 - 0x400000
		 = 0xc0000000
	and

	__va(0x100000) = 0xc0000000 + 0x100000 = 0xc0100000
	 which is what we want.

I have implemented (3) in the following patch which has same cost of
operation as the existing one.

I have tested the patches on 440x platforms only. However this should
work fine for PPC_47x also, as we only depend on the runtime address
and the current TLB XLAT entry for the startup code, which is available
in r25. I don't have access to a 47x board yet. So, it would be great if
somebody could test this on 47x.

Signed-off-by: Suzuki K. Poulose <suzuki@in.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Signed-off-by: Josh Boyer <jwboyer@gmail.com>
2011-12-20 10:21:34 -05:00
..
boot Merge remote-tracking branch 'jwb/next' into next 2011-12-16 11:24:25 +11:00
configs powerpc: Rename mapping based RELOCATABLE to DYNAMIC_MEMSTART for BookE 2011-12-20 10:20:19 -05:00
include/asm powerpc: Define virtual-physical translations for RELOCATABLE 2011-12-20 10:21:34 -05:00
kernel powerpc: Process dynamic relocations for kernel 2011-12-20 10:21:08 -05:00
kvm powerpc: Provide a way for KVM to indicate that NV GPR values are lost 2011-12-08 14:22:53 +11:00
lib powerpc: POWER7 optimised copy_to_user/copy_from_user using VMX 2011-12-19 14:40:40 +11:00
math-emu powerpc/math_emu/efp: Look for errata handler when type mismatches 2011-10-06 23:36:47 -05:00
mm powerpc: Define virtual-physical translations for RELOCATABLE 2011-12-20 10:21:34 -05:00
net net: filter: BPF 'JIT' compiler for PPC64 2011-07-21 12:38:32 -07:00
oprofile powerpc/oprofile: Handle events that raise an exception without overflowing 2011-05-26 13:38:57 +10:00
platforms Merge remote-tracking branch 'jwb/next' into next 2011-12-16 11:24:25 +11:00
sysdev Merge remote-tracking branch 'jwb/next' into next 2011-12-16 11:24:25 +11:00
xmon powerpc/xmon: Fix #if typo for systems without MSR[RI] 2011-11-25 14:11:28 +11:00
Kconfig powerpc: Process dynamic relocations for kernel 2011-12-20 10:21:08 -05:00
Kconfig.debug powerpc: Implement CONFIG_STRICT_DEVMEM 2011-11-28 11:42:08 +11:00
Makefile powerpc: Process dynamic relocations for kernel 2011-12-20 10:21:08 -05:00
relocs_check.pl powerpc: Process dynamic relocations for kernel 2011-12-20 10:21:08 -05:00