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 <[e-mail]>
[[e-mail]: make offset long and non-negative in simple case]
Signed-off-by: Scott Wood <[e-mail]>

arch/powerpc/kernel/head_fsl_booke.S

···
 	mr	r23,r3
 	mr	r25,r4
 
+	bl	0f
+0:	mflr	r8
+	addis	r3,r8,(is_second_reloc - 0b)@ha
+	lwz	r19,(is_second_reloc - 0b)@l(r3)
+
+	/* Check if this is the second relocation. */
+	cmpwi	r19,1
+	bne	1f
+
+	/*
+	 * For the second relocation, we already get the real memstart_addr
+	 * from device tree. So we will map PAGE_OFFSET to memstart_addr,
+	 * then the virtual address of start kernel should be:
+	 *          PAGE_OFFSET + (kernstart_addr - memstart_addr)
+	 * Since the offset between kernstart_addr and memstart_addr should
+	 * never be beyond 1G, so we can just use the lower 32bit of them
+	 * for the calculation.
+	 */
+	lis	r3,PAGE_OFFSET@h
+
+	addis	r4,r8,(kernstart_addr - 0b)@ha
+	addi	r4,r4,(kernstart_addr - 0b)@l
+	lwz	r5,4(r4)
+
+	addis	r6,r8,(memstart_addr - 0b)@ha
+	addi	r6,r6,(memstart_addr - 0b)@l
+	lwz	r7,4(r6)
+
+	subf	r5,r7,r5
+	add	r3,r3,r5
+	b	2f
+
+1:
 	/*
 	 * We have the runtime (virutal) address of our base.
 	 * We calculate our shift of offset from a 64M page.
···
 	subf	r3,r5,r6			/* r3 = r6 - r5 */
 	add	r3,r4,r3			/* Required Virtual Address */
 
-	bl	relocate
+2:	bl	relocate
+
+	/*
+	 * For the second relocation, we already set the right tlb entries
+	 * for the kernel space, so skip the code in fsl_booke_entry_mapping.S
+	*/
+	cmpwi	r19,1
+	beq	set_ivor
 #endif
 
 /* We try to not make any assumptions about how the boot loader
···
 #include "fsl_booke_entry_mapping.S"
 #undef ENTRY_MAPPING_BOOT_SETUP
 
+set_ivor:
 	/* Establish the interrupt vector offsets */
 	SET_IVOR(0,  CriticalInput);
 	SET_IVOR(1,  MachineCheck);
···
 	bl	early_init
 
 #ifdef CONFIG_RELOCATABLE
+	mr	r3,r30
+	mr	r4,r31
 #ifdef CONFIG_PHYS_64BIT
-	mr	r3,r23
-	mr	r4,r25
+	mr	r5,r23
+	mr	r6,r25
 #else
-	mr	r3,r25
+	mr	r5,r25
 #endif
 	bl	relocate_init
 #endif
···
 /*
  * Restore to the address space 0 and also invalidate the tlb entry created
  * by switch_to_as1.
+ * r3 - the tlb entry which should be invalidated
+ * r4 - __pa(PAGE_OFFSET in AS1) - __pa(PAGE_OFFSET in AS0)
+ * r5 - device tree virtual address. If r4 is 0, r5 is ignored.
 */
 _GLOBAL(restore_to_as0)
 	mflr	r0
···
 0:	mflr	r9
 	addi	r9,r9,1f - 0b
 
-	mfmsr	r7
+	/*
+	 * We may map the PAGE_OFFSET in AS0 to a different physical address,
+	 * so we need calculate the right jump and device tree address based
+	 * on the offset passed by r4.
+	 */
+	add	r9,r9,r4
+	add	r5,r5,r4
+
+2:	mfmsr	r7
 	li	r8,(MSR_IS | MSR_DS)
 	andc	r7,r7,r8
 
···
 	mtspr	SPRN_MAS1,r9
 	tlbwe
 	isync
+
+	cmpwi	r4,0
+	bne	3f
 	mtlr	r0
 	blr
+
+	/*
+	 * The PAGE_OFFSET will map to a different physical address,
+	 * jump to _start to do another relocation again.
+	*/
+3:	mr	r3,r5
+	bl	_start
 
 /*
  * We put a few things here that have to be page-aligned. This stuff

arch/powerpc/mm/fsl_booke_mmu.c

···
 
 	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++)
···
 }
 
 #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)
···
 	 *                              (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

arch/powerpc/mm/mmu_decl.h

···
 extern unsigned long mmu_mapin_ram(unsigned long top);
 extern void adjust_total_lowmem(void);
 extern int switch_to_as1(void);
-extern void restore_to_as0(int esel);
+extern void restore_to_as0(int esel, int offset, void *dt_ptr);
 #endif
 extern void loadcam_entry(unsigned int index);