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linux/arch/microblaze/kernel/head.S
Michal Simek ee68f1745e microblaze: Support systems without lmb bram 
When the system has no lmb bram, main memory should be start from
zero because of microblaze vectors.

DTS fragment could look like:
	DDR2_SDRAM: memory@0 {
		device_type = "memory";
		reg = < 0x0 0x10000000 >;
	} ;

Then you have to setup CONFIG_KERNEL_BASE_ADDR=0 which caused
that kernel physical start address will be zero. On reset vector place
will be jump to 0x100 and on 0x100 starts kernel text.

You have to solve how to load the kernel before cpu starts.
Tested with XMD.

Signed-off-by: Michal Simek <monstr@monstr.eu>
2010-04-01 08:38:23 +02:00

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/*
* Copyright (C) 2007-2009 Michal Simek <monstr@monstr.eu>
* Copyright (C) 2007-2009 PetaLogix
* Copyright (C) 2006 Atmark Techno, Inc.
*
* MMU code derived from arch/ppc/kernel/head_4xx.S:
* Copyright (c) 1995-1996 Gary Thomas <gdt@linuxppc.org>
* Initial PowerPC version.
* Copyright (c) 1996 Cort Dougan <cort@cs.nmt.edu>
* Rewritten for PReP
* Copyright (c) 1996 Paul Mackerras <paulus@cs.anu.edu.au>
* Low-level exception handers, MMU support, and rewrite.
* Copyright (c) 1997 Dan Malek <dmalek@jlc.net>
* PowerPC 8xx modifications.
* Copyright (c) 1998-1999 TiVo, Inc.
* PowerPC 403GCX modifications.
* Copyright (c) 1999 Grant Erickson <grant@lcse.umn.edu>
* PowerPC 403GCX/405GP modifications.
* Copyright 2000 MontaVista Software Inc.
* PPC405 modifications
* PowerPC 403GCX/405GP modifications.
* Author: MontaVista Software, Inc.
* frank_rowand@mvista.com or source@mvista.com
* debbie_chu@mvista.com
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*/
#include <linux/linkage.h>
#include <asm/thread_info.h>
#include <asm/page.h>
#include <linux/of_fdt.h> /* for OF_DT_HEADER */
#ifdef CONFIG_MMU
#include <asm/setup.h> /* COMMAND_LINE_SIZE */
#include <asm/mmu.h>
#include <asm/processor.h>
.data
.global empty_zero_page
.align 12
empty_zero_page:
.space 4096
.global swapper_pg_dir
swapper_pg_dir:
.space 4096
#endif /* CONFIG_MMU */
.text
ENTRY(_start)
#if CONFIG_KERNEL_BASE_ADDR == 0
brai TOPHYS(real_start)
.org 0x100
real_start:
#endif
mfs r1, rmsr
andi r1, r1, ~2
mts rmsr, r1
/*
* Here is checking mechanism which check if Microblaze has msr instructions
* We load msr and compare it with previous r1 value - if is the same,
* msr instructions works if not - cpu don't have them.
*/
/* r8=0 - I have msr instr, 1 - I don't have them */
rsubi r0, r0, 1 /* set the carry bit */
msrclr r0, 0x4 /* try to clear it */
/* read the carry bit, r8 will be '0' if msrclr exists */
addik r8, r0, 0
/* r7 may point to an FDT, or there may be one linked in.
if it's in r7, we've got to save it away ASAP.
We ensure r7 points to a valid FDT, just in case the bootloader
is broken or non-existent */
beqi r7, no_fdt_arg /* NULL pointer? don't copy */
lw r11, r0, r7 /* Does r7 point to a */
rsubi r11, r11, OF_DT_HEADER /* valid FDT? */
beqi r11, _prepare_copy_fdt
or r7, r0, r0 /* clear R7 when not valid DTB */
bnei r11, no_fdt_arg /* No - get out of here */
_prepare_copy_fdt:
or r11, r0, r0 /* incremment */
ori r4, r0, TOPHYS(_fdt_start)
ori r3, r0, (0x4000 - 4)
_copy_fdt:
lw r12, r7, r11 /* r12 = r7 + r11 */
sw r12, r4, r11 /* addr[r4 + r11] = r12 */
addik r11, r11, 4 /* increment counting */
bgtid r3, _copy_fdt /* loop for all entries */
addik r3, r3, -4 /* descrement loop */
no_fdt_arg:
#ifdef CONFIG_MMU
#ifndef CONFIG_CMDLINE_BOOL
/*
* handling command line
* copy command line to __init_end. There is space for storing command line.
*/
or r6, r0, r0 /* incremment */
ori r4, r0, __init_end /* load address of command line */
tophys(r4,r4) /* convert to phys address */
ori r3, r0, COMMAND_LINE_SIZE - 1 /* number of loops */
_copy_command_line:
lbu r2, r5, r6 /* r7=r5+r6 - r5 contain pointer to command line */
sb r2, r4, r6 /* addr[r4+r6]= r7*/
addik r6, r6, 1 /* increment counting */
bgtid r3, _copy_command_line /* loop for all entries */
addik r3, r3, -1 /* descrement loop */
addik r5, r4, 0 /* add new space for command line */
tovirt(r5,r5)
#endif /* CONFIG_CMDLINE_BOOL */
#ifdef NOT_COMPILE
/* save bram context */
or r6, r0, r0 /* incremment */
ori r4, r0, TOPHYS(_bram_load_start) /* save bram context */
ori r3, r0, (LMB_SIZE - 4)
_copy_bram:
lw r7, r0, r6 /* r7 = r0 + r6 */
sw r7, r4, r6 /* addr[r4 + r6] = r7*/
addik r6, r6, 4 /* increment counting */
bgtid r3, _copy_bram /* loop for all entries */
addik r3, r3, -4 /* descrement loop */
#endif
/* We have to turn on the MMU right away. */
/*
* Set up the initial MMU state so we can do the first level of
* kernel initialization. This maps the first 16 MBytes of memory 1:1
* virtual to physical.
*/
nop
addik r3, r0, 63 /* Invalidate all TLB entries */
_invalidate:
mts rtlbx, r3
mts rtlbhi, r0 /* flush: ensure V is clear */
bgtid r3, _invalidate /* loop for all entries */
addik r3, r3, -1
/* sync */
/* Setup the kernel PID */
mts rpid,r0 /* Load the kernel PID */
nop
bri 4
/*
* We should still be executing code at physical address area
* RAM_BASEADDR at this point. However, kernel code is at
* a virtual address. So, set up a TLB mapping to cover this once
* translation is enabled.
*/
addik r3,r0, CONFIG_KERNEL_START /* Load the kernel virtual address */
tophys(r4,r3) /* Load the kernel physical address */
/*
* Configure and load two entries into TLB slots 0 and 1.
* In case we are pinning TLBs, these are reserved in by the
* other TLB functions. If not reserving, then it doesn't
* matter where they are loaded.
*/
andi r4,r4,0xfffffc00 /* Mask off the real page number */
ori r4,r4,(TLB_WR | TLB_EX) /* Set the write and execute bits */
andi r3,r3,0xfffffc00 /* Mask off the effective page number */
ori r3,r3,(TLB_VALID | TLB_PAGESZ(PAGESZ_16M))
mts rtlbx,r0 /* TLB slow 0 */
mts rtlblo,r4 /* Load the data portion of the entry */
mts rtlbhi,r3 /* Load the tag portion of the entry */
addik r4, r4, 0x01000000 /* Map next 16 M entries */
addik r3, r3, 0x01000000
ori r6,r0,1 /* TLB slot 1 */
mts rtlbx,r6
mts rtlblo,r4 /* Load the data portion of the entry */
mts rtlbhi,r3 /* Load the tag portion of the entry */
/*
* Load a TLB entry for LMB, since we need access to
* the exception vectors, using a 4k real==virtual mapping.
*/
ori r6,r0,3 /* TLB slot 3 */
mts rtlbx,r6
ori r4,r0,(TLB_WR | TLB_EX)
ori r3,r0,(TLB_VALID | TLB_PAGESZ(PAGESZ_4K))
mts rtlblo,r4 /* Load the data portion of the entry */
mts rtlbhi,r3 /* Load the tag portion of the entry */
/*
* We now have the lower 16 Meg of RAM mapped into TLB entries, and the
* caches ready to work.
*/
turn_on_mmu:
ori r15,r0,start_here
ori r4,r0,MSR_KERNEL_VMS
mts rmsr,r4
nop
rted r15,0 /* enables MMU */
nop
start_here:
#endif /* CONFIG_MMU */
/* Initialize small data anchors */
la r13, r0, _KERNEL_SDA_BASE_
la r2, r0, _KERNEL_SDA2_BASE_
/* Initialize stack pointer */
la r1, r0, init_thread_union + THREAD_SIZE - 4
/* Initialize r31 with current task address */
la r31, r0, init_task
/*
* Call platform dependent initialize function.
* Please see $(ARCH)/mach-$(SUBARCH)/setup.c for
* the function.
*/
la r9, r0, machine_early_init
brald r15, r9
nop
#ifndef CONFIG_MMU
la r15, r0, machine_halt
braid start_kernel
nop
#else
/*
* Initialize the MMU.
*/
bralid r15, mmu_init
nop
/* Go back to running unmapped so we can load up new values
* and change to using our exception vectors.
* On the MicroBlaze, all we invalidate the used TLB entries to clear
* the old 16M byte TLB mappings.
*/
ori r15,r0,TOPHYS(kernel_load_context)
ori r4,r0,MSR_KERNEL
mts rmsr,r4
nop
bri 4
rted r15,0
nop
/* Load up the kernel context */
kernel_load_context:
# Keep entry 0 and 1 valid. Entry 3 mapped to LMB can go away.
ori r5,r0,3
mts rtlbx,r5
nop
mts rtlbhi,r0
nop
addi r15, r0, machine_halt
ori r17, r0, start_kernel
ori r4, r0, MSR_KERNEL_VMS
mts rmsr, r4
nop
rted r17, 0 /* enable MMU and jump to start_kernel */
nop
#endif /* CONFIG_MMU */
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