head.s

讲述linux的初始化过程

/* -*- mode: asm -*-
**
** head.S -- This file contains the initial boot code for the
**	     Linux/68k kernel.
**
** Copyright 1993 by Hamish Macdonald
**
** 68040 fixes by Michael Rausch
** 68060 fixes by Roman Hodek
** MMU cleanup by Randy Thelen
** Final MMU cleanup by Roman Zippel
**
** Atari support by Andreas Schwab, using ideas of Robert de Vries
** and Bjoern Brauel
** VME Support by Richard Hirst
**
** 94/11/14 Andreas Schwab: put kernel at PAGESIZE
** 94/11/18 Andreas Schwab: remove identity mapping of STRAM for Atari
** ++ Bjoern & Roman: ATARI-68040 support for the Medusa
** 95/11/18 Richard Hirst: Added MVME166 support
** 96/04/26 Guenther Kelleter: fixed identity mapping for Falcon with
** 			      Magnum- and FX-alternate ram
** 98/04/25 Phil Blundell: added HP300 support
** 1998/08/30 David Kilzer: Added support for fbcon_font_desc structures
**            for linux-2.1.115
** 9/02/11  Richard Zidlicky: added Q40 support (initial vesion 99/01/01) 
**
** This file is subject to the terms and conditions of the GNU General Public
** License. See the file README.legal in the main directory of this archive
** for more details.
**
*/

/*
 * Linux startup code.
 *
 * At this point, the boot loader has:
 * Disabled interrupts
 * Disabled caches
 * Put us in supervisor state.
 *
 * The kernel setup code takes the following steps:
 * .  Raise interrupt level
 * .  Set up initial kernel memory mapping.
 *    .  This sets up a mapping of the 4M of memory the kernel is located in.
 *    .  It also does a mapping of any initial machine specific areas.
 * .  Enable the MMU
 * .  Enable cache memories
 * .  Jump to kernel startup
 *
 * Much of the file restructuring was to accomplish:
 * 1) Remove register dependency through-out the file.
 * 2) Increase use of subroutines to perform functions
 * 3) Increase readability of the code
 *
 * Of course, readability is a subjective issue, so it will never be
 * argued that that goal was accomplished.  It was merely a goal.
 * A key way to help make code more readable is to give good
 * documentation.  So, the first thing you will find is exaustive
 * write-ups on the structure of the file, and the features of the
 * functional subroutines.
 *
 * General Structure:
 * ------------------
 *	Without a doubt the single largest chunk of head.S is spent
 * mapping the kernel and I/O physical space into the logical range
 * for the kernel.
 *	There are new subroutines and data structures to make MMU
 * support cleaner and easier to understand.
 * 	First, you will find a routine call "mmu_map" which maps
 * a logical to a physical region for some length given a cache
 * type on behalf of the caller.  This routine makes writing the
 * actual per-machine specific code very simple.
 *	A central part of the code, but not a subroutine in itself,
 * is the mmu_init code which is broken down into mapping the kernel
 * (the same for all machines) and mapping machine-specific I/O
 * regions.
 *	Also, there will be a description of engaging the MMU and
 * caches.
 *	You will notice that there is a chunk of code which
 * can emit the entire MMU mapping of the machine.  This is present
 * only in debug modes and can be very helpful.
 *	Further, there is a new console driver in head.S that is
 * also only engaged in debug mode.  Currently, it's only supported
 * on the Macintosh class of machines.  However, it is hoped that
 * others will plug-in support for specific machines.
 *
 * ######################################################################
 *
 * mmu_map
 * -------
 *	mmu_map was written for two key reasons.  First, it was clear
 * that it was very difficult to read the previous code for mapping
 * regions of memory.  Second, the Macintosh required such extensive
 * memory allocations that it didn't make sense to propogate the
 * existing code any further.
 *	mmu_map requires some parameters:
 *
 *	mmu_map (logical, physical, length, cache_type)
 *
 *	While this essentially describes the function in the abstract, you'll
 * find more indepth description of other parameters at the implementation site.
 * 
 * mmu_get_root_table_entry
 * ------------------------
 * mmu_get_ptr_table_entry
 * -----------------------
 * mmu_get_page_table_entry
 * ------------------------
 * 
 *	These routines are used by other mmu routines to get a pointer into
 * a table, if necessary a new table is allocated. These routines are working
 * basically like pmd_alloc() and pte_alloc() in <asm/pgtable.h>. The root
 * table needs of course only to be allocated once in mmu_get_root_table_entry,
 * so that here also some mmu specific initialization is done. The second page
 * at the start of the kernel (the first page is unmapped later) is used for
 * the kernel_pg_dir. It must be at a position known at link time (as it's used
 * to initialize the init task struct) and since it needs special cache
 * settings, it's the easiest to use this page, the rest of the page is used
 * for further pointer tables.
 * mmu_get_page_table_entry allocates always a whole page for page tables, this
 * means 1024 pages and so 4MB of memory can be mapped. It doesn't make sense
 * to manage page tables in smaller pieces as nearly all mappings have that
 * size.
 *
 * ######################################################################
 *
 *
 * ######################################################################
 *
 * mmu_engage
 * ----------
 *	Thanks to a small helping routine enabling the mmu got quiet simple
 * and there is only one way left. mmu_engage makes a complete a new mapping
 * that only includes the absolute necessary to be able to jump to the final
 * postion and to restore the original mapping.
 * As this code doesn't need a transparent translation register anymore this
 * means all registers are free to be used by machines that needs them for
 * other purposes.
 *
 * ######################################################################
 *
 * mmu_print
 * ---------
 *	This algorithm will print out the page tables of the system as
 * appropriate for an 030 or an 040.  This is useful for debugging purposes
 * and as such is enclosed in #ifdef MMU_PRINT/#endif clauses.
 *
 * ######################################################################
 *
 * console_init
 * ------------
 *	The console is also able to be turned off.  The console in head.S
 * is specifically for debugging and can be very useful.  It is surrounded by
 * #ifdef CONSOLE/#endif clauses so it doesn't have to ship in known-good
 * kernels.  It's basic algorithm is to determine the size of the screen
 * (in height/width and bit depth) and then use that information for
 * displaying an 8x8 font or an 8x16 (widthxheight).  I prefer the 8x8 for
 * debugging so I can see more good data.  But it was trivial to add support
 * for both fonts, so I included it.
 *	Also, the algorithm for plotting pixels is abstracted so that in
 * theory other platforms could add support for different kinds of frame
 * buffers.  This could be very useful.
 *
 * console_put_penguin
 * -------------------
 *	An important part of any Linux bring up is the penguin and there's
 * nothing like getting the Penguin on the screen!  This algorithm will work
 * on any machine for which there is a console_plot_pixel.
 *
 * console_scroll
 * --------------
 *	My hope is that the scroll algorithm does the right thing on the
 * various platforms, but it wouldn't be hard to add the test conditions
 * and new code if it doesn't.
 *
 * console_putc
 * -------------
 *
 * ######################################################################
 *
 *	Register usage has greatly simplified within head.S. Every subroutine
 * saves and restores all registers that it modifies (except it returns a
 * value in there of course). So the only register that needs to be initialized
 * is the stack pointer.
 * All other init code and data is now placed in the init section, so it will
 * be automatically freed at the end of the kernel initialization.
 *
 * ######################################################################
 *
 * options
 * -------
 *	There are many options availble in a build of this file.  I've
 * taken the time to describe them here to save you the time of searching
 * for them and trying to understand what they mean.
 *
 * CONFIG_xxx:	These are the obvious machine configuration defines created
 * during configuration.  These are defined in include/linux/autoconf.h.
 *
 * CONSOLE:	There is support for head.S console in this file.  This
 * console can talk to a Mac frame buffer, but could easily be extrapolated
 * to extend it to support other platforms.
 *
 * TEST_MMU:	This is a test harness for running on any given machine but
 * getting an MMU dump for another class of machine.  The classes of machines
 * that can be tested are any of the makes (Atari, Amiga, Mac, VME, etc.)
 * and any of the models (030, 040, 060, etc.).
 *
 *	NOTE:	TEST_MMU is NOT permanent!  It is scheduled to be removed
 *		When head.S boots on Atari, Amiga, Macintosh, and VME
 *		machines.  At that point the underlying logic will be
 *		believed to be solid enough to be trusted, and TEST_MMU
 *		can be dropped.  Do note that that will clean up the
 *		head.S code significantly as large blocks of #if/#else
 *		clauses can be removed.
 *
 * MMU_NOCACHE_KERNEL:	On the Macintosh platform there was an inquiry into
 * determing why devices don't appear to work.  A test case was to remove
 * the cacheability of the kernel bits.
 *
 * MMU_PRINT:	There is a routine built into head.S that can display the
 * MMU data structures.  It outputs its result through the serial_putc
 * interface.  So where ever that winds up driving data, that's where the
 * mmu struct will appear.  On the Macintosh that's typically the console.
 *
 * SERIAL_DEBUG:	There are a series of putc() macro statements
 * scattered through out the code to give progress of status to the
 * person sitting at the console.  This constant determines whether those
 * are used.
 *
 * DEBUG:	This is the standard DEBUG flag that can be set for building
 *		the kernel.  It has the effect adding additional tests into
 *		the code.
 *
 * FONT_6x11:
 * FONT_8x8:
 * FONT_8x16:
 *		In theory these could be determined at run time or handed
 *		over by the booter.  But, let's be real, it's a fine hard
 *		coded value.  (But, you will notice the code is run-time
 *		flexible!)  A pointer to the font's struct fbcon_font_desc
 *		is kept locally in Lconsole_font.  It is used to determine
 *		font size information dynamically.
 *
 * Atari constants:
 * USE_PRINTER:	Use the printer port for serial debug.
 * USE_SCC_B:	Use the SCC port A (Serial2) for serial debug.
 * USE_SCC_A:	Use the SCC port B (Modem2) for serial debug.
 * USE_MFP:	Use the ST-MFP port (Modem1) for serial debug.
 *
 * Macintosh constants:
 * MAC_SERIAL_DEBUG:	Turns on serial debug output for the Macintosh.
 * MAC_USE_SCC_A:	Use the SCC port A (modem) for serial debug.
 * MAC_USE_SCC_B:	Use the SCC port B (printer) for serial debug (default).
 */

#include <linux/config.h>
#include <linux/linkage.h>
#include <linux/init.h>
#include <asm/bootinfo.h>
#include <asm/setup.h>
#include <asm/entry.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include "m68k_defs.h"

#ifdef CONFIG_MAC

#include <asm/machw.h>

/*
 * Macintosh console support
 */

#define CONSOLE

/*
 * Macintosh serial debug support; outputs boot info to the printer
 *   and/or modem serial ports
 */
#undef MAC_SERIAL_DEBUG

/*
 * Macintosh serial debug port selection; define one or both;
 *   requires MAC_SERIAL_DEBUG to be defined
 */
#define MAC_USE_SCC_A		/* Macintosh modem serial port */
#define MAC_USE_SCC_B		/* Macintosh printer serial port */

#endif	/* CONFIG_MAC */

#undef MMU_PRINT
#undef MMU_NOCACHE_KERNEL
#define SERIAL_DEBUG
#undef DEBUG

/*
 * For the head.S console, there are three supported fonts, 6x11, 8x16 and 8x8.
 * The 8x8 font is harder to read but fits more on the screen.
 */
#define FONT_8x8 	/* default */
/* #define FONT_8x16 */	/* 2nd choice */
/* #define FONT_6x11 */	/* 3rd choice */

.globl SYMBOL_NAME(kernel_pg_dir)
.globl SYMBOL_NAME(availmem)
.globl SYMBOL_NAME(m68k_pgtable_cachemode)
.globl SYMBOL_NAME(m68k_supervisor_cachemode)
#ifdef CONFIG_MVME16x
.globl SYMBOL_NAME(mvme_bdid)
#endif
#ifdef CONFIG_Q40
.globl SYMBOL_NAME(q40_mem_cptr)	
#endif		

CPUTYPE_040	= 1	/* indicates an 040 */
CPUTYPE_060	= 2	/* indicates an 060 */
CPUTYPE_0460	= 3	/* if either above are set, this is set */
CPUTYPE_020	= 4	/* indicates an 020 */

/* Translation control register */
TC_ENABLE = 0x8000
TC_PAGE8K = 0x4000
TC_PAGE4K = 0x0000

/* Transparent translation registers */
TTR_ENABLE	= 0x8000	/* enable transparent translation */
TTR_ANYMODE	= 0x4000	/* user and kernel mode access */
TTR_KERNELMODE	= 0x2000	/* only kernel mode access */
TTR_USERMODE	= 0x0000	/* only user mode access */
TTR_CI		= 0x0400	/* inhibit cache */
TTR_RW		= 0x0200	/* read/write mode */
TTR_RWM		= 0x0100	/* read/write mask */
TTR_FCB2	= 0x0040	/* function code base bit 2 */
TTR_FCB1	= 0x0020	/* function code base bit 1 */
TTR_FCB0	= 0x0010	/* function code base bit 0 */
TTR_FCM2	= 0x0004	/* function code mask bit 2 */
TTR_FCM1	= 0x0002	/* function code mask bit 1 */
TTR_FCM0	= 0x0001	/* function code mask bit 0 */

/* Cache Control registers */
CC6_ENABLE_D	= 0x80000000	/* enable data cache (680[46]0) */
CC6_FREEZE_D	= 0x40000000	/* freeze data cache (68060) */
CC6_ENABLE_SB	= 0x20000000	/* enable store buffer (68060) */
CC6_PUSH_DPI	= 0x10000000	/* disable CPUSH invalidation (68060) */
CC6_HALF_D	= 0x08000000	/* half-cache mode for data cache (68060) */
CC6_ENABLE_B	= 0x00800000	/* enable branch cache (68060) */
CC6_CLRA_B	= 0x00400000	/* clear all entries in branch cache (68060) */
CC6_CLRU_B	= 0x00200000	/* clear user entries in branch cache (68060) */
CC6_ENABLE_I	= 0x00008000	/* enable instruction cache (680[46]0) */
CC6_FREEZE_I	= 0x00004000	/* freeze instruction cache (68060) */
CC6_HALF_I	= 0x00002000	/* half-cache mode for instruction cache (68060) */
CC3_ALLOC_WRITE	= 0x00002000	/* write allocate mode(68030) */
CC3_ENABLE_DB	= 0x00001000	/* enable data burst (68030) */
CC3_CLR_D	= 0x00000800	/* clear data cache (68030) */
CC3_CLRE_D	= 0x00000400	/* clear entry in data cache (68030) */
CC3_FREEZE_D	= 0x00000200	/* freeze data cache (68030) */
CC3_ENABLE_D	= 0x00000100	/* enable data cache (68030) */
CC3_ENABLE_IB	= 0x00000010	/* enable instruction burst (68030) */
CC3_CLR_I	= 0x00000008	/* clear instruction cache (68030) */
CC3_CLRE_I	= 0x00000004	/* clear entry in instruction cache (68030) */
CC3_FREEZE_I	= 0x00000002	/* freeze instruction cache (68030) */
CC3_ENABLE_I	= 0x00000001	/* enable instruction cache (68030) */

/* Miscellaneous definitions */
PAGESIZE	= 4096
PAGESHIFT	= 12

ROOT_TABLE_SIZE	= 128
PTR_TABLE_SIZE	= 128
PAGE_TABLE_SIZE	= 64
ROOT_INDEX_SHIFT = 25
PTR_INDEX_SHIFT  = 18
PAGE_INDEX_SHIFT = 12

#ifdef DEBUG
/* When debugging use readable names for labels */
#ifdef __STDC__
#define L(name) .head.S.##name
#else
#define L(name) .head.S./**/name
#endif
#else
#ifdef __STDC__
#define L(name) .L##name
#else
#define L(name) .L/**/name
#endif
#endif

/* The __INITDATA stuff is a no-op when ftrace or kgdb are turned on */
#ifndef __INITDATA
#define __INITDATA	.data
#define __FINIT		.previous
#endif

/* Several macros to make the writing of subroutines easier:
 * - func_start marks the beginning of the routine which setups the frame
 *   register and saves the registers, it also defines another macro
 *   to automatically restore the registers again.
 * - func_return marks the end of the routine and simply calls the prepared
 *   macro to restore registers and jump back to the caller.
 * - func_define generates another macro to automatically put arguments
 *   onto the stack call the subroutine and cleanup the stack again.
 */

/* Within subroutines these macros can be used to access the arguments
 * on the stack. With STACK some allocated memory on the stack can be
 * accessed and ARG0 points to the return address (used by mmu_engage).
 */
#define	STACK	%a6@(stackstart)
#define ARG0	%a6@(4)
#define ARG1	%a6@(8)
#define ARG2	%a6@(12)
#define ARG3	%a6@(16)
#define ARG4	%a6@(20)

.macro	func_start	name,saveregs,stack=0
L(\name):
	linkw	%a6,#-\stack
	moveml	\saveregs,%sp@-
.set	stackstart,-\stack	

.macro	func_return_\name
	moveml	%sp@+,\saveregs
	unlk	%a6
	rts
.endm
.endm

.macro	func_return	name
	func_return_\name
.endm

.macro	func_call	name
	jbsr	L(\name)
.endm

.macro	move_stack	nr,arg1,arg2,arg3,arg4
.if	\nr
	move_stack	"(\nr-1)",\arg2,\arg3,\arg4
	movel	\arg1,%sp@-
.endif
.endm

.macro	func_define	name,nr=0
.macro	\name	arg1,arg2,arg3,arg4
	move_stack	\nr,\arg1,\arg2,\arg3,\arg4
	func_call	\name
.if	\nr
	lea	%sp@(\nr*4),%sp
.endif
.endm
.endm

func_define	mmu_map,4
func_define	mmu_map_tt,4
func_define	mmu_fixup_page_mmu_cache,1
func_define	mmu_temp_map,2
func_define	mmu_engage
func_define	mmu_get_root_table_entry,1
func_define	mmu_get_ptr_table_entry,2
func_define	mmu_get_page_table_entry,2
func_define	mmu_print
func_define	get_new_page
#ifdef CONFIG_HP300
func_define	set_leds
#endif

.macro	mmu_map_eq	arg1,arg2,arg3
	mmu_map	\arg1,\arg1,\arg2,\arg3
.endm

.macro	get_bi_record	record
	pea	\record
	func_call	get_bi_record
	addql	#4,%sp
.endm

func_define	serial_putc,1
func_define	console_putc,1

.macro	putc	ch
#if defined(CONSOLE) || defined(SERIAL_DEBUG)
	pea	\ch
#endif
#ifdef CONSOLE
	func_call	console_putc
#endif
#ifdef SERIAL_DEBUG
	func_call	serial_putc
#endif
#if defined(CONSOLE) || defined(SERIAL_DEBUG)
	addql	#4,%sp
#endif
.endm

.macro	dputc	ch
#ifdef DEBUG
	putc	\ch
#endif
.endm

func_define	putn,1

.macro	dputn	nr
#ifdef DEBUG
	putn	\nr
#endif
.endm

.macro	puts		string
#if defined(CONSOLE) || defined(SERIAL_DEBUG)
	__INITDATA
.Lstr\@:
	.string	"\string"
	__FINIT
	pea	%pc@(.Lstr\@)
	func_call	puts
	addql	#4,%sp
#endif
.endm

.macro	dputs	string
#ifdef DEBUG
	puts	"\string"
#endif
.endm

#define is_not_amiga(lab) cmpl &MACH_AMIGA,%pc@(m68k_machtype); jne lab
#define is_not_atari(lab) cmpl &MACH_ATARI,%pc@(m68k_machtype); jne lab
#define is_not_mac(lab) cmpl &MACH_MAC,%pc@(m68k_machtype); jne lab
#define is_not_mvme147(lab) cmpl &MACH_MVME147,%pc@(m68k_machtype); jne lab
#define is_not_mvme16x(lab) cmpl &MACH_MVME16x,%pc@(m68k_machtype); jne lab
#define is_not_bvme6000(lab) cmpl &MACH_BVME6000,%pc@(m68k_machtype); jne lab
#define is_mvme147(lab) cmpl &MACH_MVME147,%pc@(m68k_machtype); jeq lab
#define is_mvme16x(lab) cmpl &MACH_MVME16x,%pc@(m68k_machtype); jeq lab
#define is_bvme6000(lab) cmpl &MACH_BVME6000,%pc@(m68k_machtype); jeq lab
#define is_not_hp300(lab) cmpl &MACH_HP300,%pc@(m68k_machtype); jne lab
#define is_not_apollo(lab) cmpl &MACH_APOLLO,%pc@(m68k_machtype); jne lab
#define is_not_q40(lab) cmpl &MACH_Q40,%pc@(m68k_machtype); jne lab
#define is_not_sun3x(lab) cmpl &MACH_SUN3X,%pc@(m68k_machtype); jne lab