2 files changed, 89 insertions, 3 deletions

diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index f149967ee6b5..f072e974f8a2 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -97,12 +97,26 @@ extern unsigned int HPAGE_SHIFT;
 
 extern phys_addr_t memstart_addr;
 extern phys_addr_t kernstart_addr;
+
+#ifdef CONFIG_RELOCATABLE_PPC32
+extern long long virt_phys_offset;
 #endif
+
+#endif /* __ASSEMBLY__ */
 #define PHYSICAL_START  kernstart_addr
-#else
+
+#else   /* !CONFIG_NONSTATIC_KERNEL */
 #define PHYSICAL_START  ASM_CONST(CONFIG_PHYSICAL_START)
 #endif
 
+/* See Description below for VIRT_PHYS_OFFSET */
+#ifdef CONFIG_RELOCATABLE_PPC32
+#define VIRT_PHYS_OFFSET virt_phys_offset
+#else
+#define VIRT_PHYS_OFFSET (KERNELBASE - PHYSICAL_START)
+#endif
+
+
 #ifdef CONFIG_PPC64
 #define MEMORY_START    0UL
 #elif defined(CONFIG_NONSTATIC_KERNEL)
@@ -125,12 +139,77 @@ extern phys_addr_t kernstart_addr;
  * determine MEMORY_START until then.  However we can determine PHYSICAL_START
  * from information at hand (program counter, TLB lookup).
  *
+ * On BookE with RELOCATABLE (RELOCATABLE_PPC32)
+ *
+ *   With RELOCATABLE_PPC32,  we support loading the kernel at any physical 
+ *   address without any restriction on the page alignment.
+ *
+ *   We find the runtime address of _stext and relocate ourselves based on 
+ *   the following calculation:
+ *
+ *        virtual_base = ALIGN_DOWN(KERNELBASE,256M) +
+ *                              MODULO(_stext.run,256M)
+ *   and create the following mapping:
+ *
+ *        ALIGN_DOWN(_stext.run,256M) => ALIGN_DOWN(KERNELBASE,256M)
+ *
+ *   When we process relocations, we cannot depend on the
+ *   existing equation for the __va()/__pa() translations:
+ *
+ *         __va(x) = (x)  - PHYSICAL_START + KERNELBASE
+ *
+ *   Where:
+ *       PHYSICAL_START = kernstart_addr = Physical address of _stext
+ *       KERNELBASE = Compiled virtual address of _stext.
+ *
+ *   This formula holds true iff, kernel load address is TLB page aligned.
+ *
+ *   In our case, we need to also account for the shift in the kernel Virtual 
+ *   address.
+ *
+ *   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.
+ *
+ *   Rather, it should be : 0xc0000000 + 0x100000 = 0xc0100000
+ *              according to our mapping.
+ *
+ *   Hence we use the following formula to get the translations right:
+ *
+ *        __va(x) = (x) - [ PHYSICAL_START - Effective KERNELBASE ]
+ *
+ *        Where :
+ *              PHYSICAL_START = dynamic load address.(kernstart_addr variable)
+ *              Effective KERNELBASE = virtual_base =
+ *                                   = ALIGN_DOWN(KERNELBASE,256M) +
+ *                                              MODULO(PHYSICAL_START,256M)
+ *
+ *      To make the cost of __va() / __pa() more light weight, we introduce
+ *      a new variable virt_phys_offset, which will hold :
+ *
+ *      virt_phys_offset = Effective KERNELBASE - PHYSICAL_START
+ *                       = ALIGN_DOWN(KERNELBASE,256M) - 
+ *                              ALIGN_DOWN(PHYSICALSTART,256M)
+ *
+ *      Hence :
+ *
+ *      __va(x) = x - PHYSICAL_START + Effective KERNELBASE
+ *              = x + virt_phys_offset
+ *
+ *              and
+ *      __pa(x) = x + PHYSICAL_START - Effective KERNELBASE
+ *              = x - virt_phys_offset
+ *              
  * On non-Book-E PPC64 PAGE_OFFSET and MEMORY_START are constants so use
  * the other definitions for __va & __pa.
  */
 #ifdef CONFIG_BOOKE
-#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) - PHYSICAL_START + KERNELBASE))
-#define __pa(x) ((unsigned long)(x) + PHYSICAL_START - KERNELBASE)
+#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + VIRT_PHYS_OFFSET))
+#define __pa(x) ((unsigned long)(x) - VIRT_PHYS_OFFSET)
 #else
 #define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + PAGE_OFFSET - MEMORY_START))
 #define __pa(x) ((unsigned long)(x) - PAGE_OFFSET + MEMORY_START)
diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
index 161cefde5c15..60a4e4e84e8c 100644
--- a/arch/powerpc/mm/init_32.c
+++ b/arch/powerpc/mm/init_32.c
@@ -65,6 +65,13 @@ phys_addr_t memstart_addr = (phys_addr_t)~0ull;
 EXPORT_SYMBOL(memstart_addr);
 phys_addr_t kernstart_addr;
 EXPORT_SYMBOL(kernstart_addr);
+
+#ifdef CONFIG_RELOCATABLE_PPC32
+/* Used in __va()/__pa() */
+long long virt_phys_offset;
+EXPORT_SYMBOL(virt_phys_offset);
+#endif
+
 phys_addr_t lowmem_end_addr;
 
 int boot_mapsize;