x86: Split sc520 memory sizing versus reporting

This patch allows the low-level assembler boot-strap to obtain the RAM
size without calling the destructive 'sizer' routine. This allows
boot-strapping from a U-Boot image loaded in RAM

Signed-off-by: Graeme Russ <graeme.russ@gmail.com>

arch/i386/cpu/sc520/sc520_asm.S

@@ -498,47 +498,21 @@ bad_ram:
 
 dram_done:
 
-	/* readback DRCBENDADR and return the number
-	 * of available ram bytes in %eax */
-
-	movl    $DRCBENDADR, %edi        /* DRAM ending address register  */
-
-bank0:	movl	(%edi), %eax
-	movl	%eax, %ecx
-	andl	$0x00000080, %ecx
-	jz	bank1
-	andl	$0x0000007f, %eax
-	shll	$22, %eax
-	movl	%eax, %ebx
-
-bank1:	movl	(%edi), %eax
-	movl	%eax, %ecx
-	andl	$0x00008000, %ecx
-	jz	bank2
-	andl	$0x00007f00, %eax
-	shll	$14, %eax
-	movl	%eax, %ebx
-
-bank2:	movl	(%edi), %eax
-	movl	%eax, %ecx
-	andl	$0x00800000, %ecx
-	jz	bank3
-	andl	$0x007f0000, %eax
-	shll	$6, %eax
-	movl	%eax, %ebx
+#if CONFIG_SYS_SDRAM_ECC_ENABLE
+	/*
+	 * We are in the middle of an existing 'call' - Need to store the
+	 * existing return address before making another 'call'
+	 */
+	movl	%ebp, %ebx
 
-bank3:	movl	(%edi), %eax
-	movl	%eax, %ecx
-	andl	$0x80000000, %ecx
-	jz	done
-	andl	$0x7f000000, %eax
-	shrl	$2, %eax
-	movl	%eax, %ebx
+	/* Get the memory size */
+	movl	$init_ecc, %ebp
+	jmpl	get_mem_size
 
-done:
-	movl	%ebx, %eax
+init_ecc:
+	/* Restore the orignal return address */
+	movl	%ebx, %ebp
 
-#if CONFIG_SYS_SDRAM_ECC_ENABLE
 	/* A nominal memory test: just a byte at each address line */
 	movl    %eax, %ecx
 	shrl    $0x1, %ecx
@@ -575,6 +549,50 @@ set_ecc:
 	mov	$0x05, %al
 	movb    %al, (%edi)
 #endif
+
 out:
+	jmp	*%ebp
+
+/*
+ * Read and decode the sc520 DRCBENDADR MMCR and return the number of
+ * available ram bytes in %eax
+ */
+.globl get_mem_size
+get_mem_size:
+	movl    $DRCBENDADR, %edi        /* DRAM ending address register  */
+
+bank0:	movl	(%edi), %eax
+	movl	%eax, %ecx
+	andl	$0x00000080, %ecx
+	jz	bank1
+	andl	$0x0000007f, %eax
+	shll	$22, %eax
+	movl	%eax, %ebx
+
+bank1:	movl	(%edi), %eax
+	movl	%eax, %ecx
+	andl	$0x00008000, %ecx
+	jz	bank2
+	andl	$0x00007f00, %eax
+	shll	$14, %eax
+	movl	%eax, %ebx
+
+bank2:	movl	(%edi), %eax
+	movl	%eax, %ecx
+	andl	$0x00800000, %ecx
+	jz	bank3
+	andl	$0x007f0000, %eax
+	shll	$6, %eax
+	movl	%eax, %ebx
+
+bank3:	movl	(%edi), %eax
+	movl	%eax, %ecx
+	andl	$0x80000000, %ecx
+	jz	done
+	andl	$0x7f000000, %eax
+	shrl	$2, %eax
+	movl	%eax, %ebx
+
+done:
 	movl	%ebx, %eax
 	jmp	*%ebp

arch/i386/cpu/start.S

@@ -63,6 +63,11 @@ early_board_init_ret:
 	jmp     mem_init
 mem_init_ret:
 
+	/* fetch memory size (into %eax) */
+	mov	$get_mem_size_ret, %ebp
+	jmp     get_mem_size
+get_mem_size_ret:
+
 	/* Check we have enough memory for stack */
 	movl	$CONFIG_SYS_STACK_SIZE, %ecx
 	cmpl	%ecx, %eax