powerpc/fsl_booke: make sure PAGE_OFFSET map to memstart_addr for relocatable kernel

This is always true for a non-relocatable kernel. Otherwise the kernel
would get stuck. But for a relocatable kernel, it seems a little
complicated. When booting a relocatable kernel, we just align the
kernel start addr to 64M and map the PAGE_OFFSET from there. The
relocation will base on this virtual address. But if this address
is not the same as the memstart_addr, we will have to change the
map of PAGE_OFFSET to the real memstart_addr and do another relocation
again.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
[scottwood@freescale.com: make offset long and non-negative in simple case]
Signed-off-by: Scott Wood <scottwood@freescale.com>

arch/powerpc/mm/fsl_booke_mmu.c

@@ -231,7 +231,7 @@ void __init adjust_total_lowmem(void)
 
 	i = switch_to_as1();
 	__max_low_memory = map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM);
-	restore_to_as0(i);
+	restore_to_as0(i, 0, 0);
 
 	pr_info("Memory CAM mapping: ");
 	for (i = 0; i < tlbcam_index - 1; i++)
@@ -252,17 +252,25 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
 }
 
 #ifdef CONFIG_RELOCATABLE
-notrace void __init relocate_init(phys_addr_t start)
+int __initdata is_second_reloc;
+notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
 {
 	unsigned long base = KERNELBASE;
 
+	kernstart_addr = start;
+	if (is_second_reloc) {
+		virt_phys_offset = PAGE_OFFSET - memstart_addr;
+		return;
+	}
+
 	/*
 	 * Relocatable kernel support based on processing of dynamic
-	 * relocation entries.
-	 * Compute the virt_phys_offset :
+	 * relocation entries. Before we get the real memstart_addr,
+	 * We will compute the virt_phys_offset like this:
 	 * virt_phys_offset = stext.run - kernstart_addr
 	 *
-	 * stext.run = (KERNELBASE & ~0x3ffffff) + (kernstart_addr & 0x3ffffff)
+	 * stext.run = (KERNELBASE & ~0x3ffffff) +
+	 *				(kernstart_addr & 0x3ffffff)
 	 * When we relocate, we have :
 	 *
 	 *	(kernstart_addr & 0x3ffffff) = (stext.run & 0x3ffffff)
@@ -272,10 +280,32 @@ notrace void __init relocate_init(phys_addr_t start)
 	 *                              (kernstart_addr & ~0x3ffffff)
 	 *
 	 */
-	kernstart_addr = start;
 	start &= ~0x3ffffff;
 	base &= ~0x3ffffff;
 	virt_phys_offset = base - start;
+	early_get_first_memblock_info(__va(dt_ptr), NULL);
+	/*
+	 * We now get the memstart_addr, then we should check if this
+	 * address is the same as what the PAGE_OFFSET map to now. If
+	 * not we have to change the map of PAGE_OFFSET to memstart_addr
+	 * and do a second relocation.
+	 */
+	if (start != memstart_addr) {
+		int n;
+		long offset = start - memstart_addr;
+
+		is_second_reloc = 1;
+		n = switch_to_as1();
+		/* map a 64M area for the second relocation */
+		if (memstart_addr > start)
+			map_mem_in_cams(0x4000000, CONFIG_LOWMEM_CAM_NUM);
+		else
+			map_mem_in_cams_addr(start, PAGE_OFFSET + offset,
+					0x4000000, CONFIG_LOWMEM_CAM_NUM);
+		restore_to_as0(n, offset, __va(dt_ptr));
+		/* We should never reach here */
+		panic("Relocation error");
+	}
 }
 #endif
 #endif